Communication device for reducing latency in a group communication network

ABSTRACT

A method and apparatus for reducing perceived latency in a group communication network provides for receiving a request from a user of a communication device wishing to initiate a group call, receiving media from the user before completely processing the request, and buffering the received media for later transmission.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.09/518,776, filed Mar. 3, 2000, pending, which application isincorporated herein by reference in its entirety.

FEDERAL RESEARCH STATEMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided by the terms of MDA904-96-G-0035awarded by the National Security Agency.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to point to multi-point communicationssystems. More specifically, the present invention relates to anapparatus and method to reduce perceived latency for users of apush-to-talk communication device in a group communication network.

II. Description of the Related Art

Point-to-multipoint communication systems have been used to providecommunications generally between a central location and multiple usersof the system. For example, dispatch systems using Land Mobile Radios(LMRs) have been used in trucks, taxis, buses, and other vehicles inorder to communicate scheduling information between a central dispatchcenter and one or more corresponding fleet vehicles. Communications maybe directed at a specific vehicle in the fleet or to all vehiclessimultaneously.

Another example of a point-to-multipoint communication system is awireless push-to-talk system. Such a system allows a group ofindividuals, each having a wireless communication device, to communicatewith other members of the group. Typically, a push-to-talk system relieson a single frequency, or dedicated channel, over which communicationsare received by the wireless communication devices. In most systems,only one member may transmit information to the other members at a time.However, all members can listen to the dedicated broadcast channel toreceive communications from the single member who is transmitting.Members desiring to transmit to other members of the system typicallysends an access request by depressing a push-to-talk button on theirrespective communication device that allows the user sole access to thededicated channel.

Push-to-talk systems are typically used in outdoor settings where agroup of people, or members, require communications with each other in a“point-to-multipoint” fashion. Examples of push-to-talk system usesinclude workgroup communications, security communications, constructionsite communication, and localized military communications. The group ofpeople requiring communications with each other is commonly known as a“net,” each member of the net sometimes referred to as a “net member.”

In a typical push-to-talk system, a dedicated channel, sometimesreferred to as a broadcast channel, is used to transmit communicationsfrom one member to multiple other members of the net simultaneously. Thededicated channel may comprise a single channel or frequency, or a groupof individual channels managed by a controller to imitate the singlechannel. In either case, only one member may transmit voice and/or datacommunications to the other member users at any given time. If anothermember attempts to transmit over the broadcast channel while anothermember is transmitting, interference between the two competingcommunications will occur, resulting in non-intelligible communicationsbeing received by the other net members.

SUMMARY OF THE INVENTION

The disclosed embodiments provide a novel and improved method andapparatus for reducing perceived latency in a group communicationnetwork. In one aspect of the invention, a method for reducing latencyin a group communication network includes the steps of determiningwhether any media frame belonging to a communication protocol is lostand, if a media frame is determined to be lost, modifying thecommunication protocol.

In another aspect of the invention, a method for reducing latency in agroup communication network includes receiving a request from a user ofa communication device wishing to initiate a group call, receiving mediafrom the user before completely processing the request, and bufferingthe received media for later transmission.

In another aspect of the invention, a communication device for reducinglatency in a group communication network includes a receiver to receivea request from a user who wishes to initiate a group call, a memory unitto buffer media that is received from the user before the request iscompletely processed, a transmitter for transmitting the buffered datato the controller after the request is processed, and a processor forprocessing the received request and the media. In one aspect, thecommunication device is a push-to-talk (PTT) device.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings in which like reference charactersidentify correspondingly throughout and wherein:

FIG. 1 illustrates a net broadcast system.

FIG. 2 illustrates a NBS net and how communication devices interact witha communications manager (CM) 104.

FIG. 3 illustrates a functional block diagram of the CM.

FIG. 4 illustrates an example of a NBS SIP signaling protocol stack.

FIG. 5 illustrates an NBS media signaling protocol stack.

FIG. 6 illustrates real time protocol voice media protocol stack.

FIG. 7 illustrates a UDP voice media protocol stack.

FIG. 8 illustrates a media traffic protocol stack.

FIG. 9 illustrates a DNS client protocol stack.

FIG. 10 illustrates the high level functionality of the group servicesmodule 500 of the CD.

FIG. 11 illustrates SIP call signaling 350.

FIG. 12 illustrates a media signaling message sequence.

FIG. 13 illustrates the sequence of media signaling messages withrespect to dormancy.

FIG. 14 illustrates a sequence of NBS media signaling messages.

FIG. 15 illustrates a state diagram of the CM 104.

FIG. 16 illustrates a state diagram of the CD 352.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The net broadcast service (NBS) system enables Internet Protocol (IP)communication devices to participate in a group voice and dataconference. NBS is primarily a Voice over IP (VoIP) application. Voicecommunication is transmitted from a talker endpoint communication deviceto one or more listeners by encapsulating voice frames in IP datagrams.Data with voice may also be transmitted in this manner. The NBS systemis described in U.S. patent application Ser. No. 09/518,622, filed Mar.3, 2000 and U.S. patent application Ser. No. 09/518,985, filed Mar. 3,2000, and are specifically incorporated by reference herein.

FIG. 1 illustrates a functional block diagram of a group communicationsystem 10. The group communication system 10 is also known as apush-to-talk system, a net broadcast service (NBS), a dispatch system,or a point-to-multi-point communication system. A definingcharacteristic of such the NBS system is that, generally, only one usermay transmit information to other users at any given time. In the NBS10, a group of communication device users, individually known as netmembers, communicate with one another using a communication deviceassigned to each net member.

The term “net” denotes a group of communication device users authorizedto communicate with each other. Generally, a central database containsinformation identifying the members of each particular net. More thanone net may operate in the same communication system. For instance, afirst net may be defined having ten members and a second net may bedefined, having twenty members. The ten members of the first net cancommunicate with each other, but generally not to members of the secondnet. In other situations, members of different nets are able to monitorcommunications between members of more than one net, but are only ableto transmit information to members within their own net.

The net operates over an existing communications system, withoutrequiring substantial changes to the existing infrastructure. Thus, acontroller and users on a net may operate in any system capable oftransmitting and receiving packet information using Internet Protocol(IP), such as a Code Division Multiple Access (CDMA) system, a TimeDivision Multiple Access (TDMA) system, a Global System for MobileCommunications (GSM) system, satellite communication systems such asGlobalstar™ or Iradiumm™, or a variety of other systems.

Net members communicate with each other using an assigned communicationdevice, shown as communication devices (CD) 12, 14, 16 and 17. CDs 12,14, 16 and 17 may be wireline or wireless communication devices such asterrestrial wireless telephones, wireline telephones having push-to-talkcapability, satellite telephones equipped with push-to-talkfunctionality, wireless video cameras, still cameras, audio devices suchas music recorders or players, laptop or desktop computers, pagingdevices, or any combination thereof. For example, the CD 12 may comprisea wireless terrestrial telephone having a video camera and display.Furthermore, each CD may be able to send and receive information ineither a secure mode, or a non-secure (clear) mode. Throughout thefollowing discussion, reference to an individual CD may be expressed bya wireless push-to-talk phone. However, it should be understood thatreference to a CD is not intended to be limited as such, and mayencompass other communication devices that have the capability totransmit and receive packet information in accordance with InternetProtocol (IP).

In the NBS system 100 of FIG. 2, a transmission privilege is definedthat generally allows a single user to transmit information to other netmembers at any given time. The transmission privilege is granted ordenied to requesting net members, depending on whether or not thetransmission privilege is currently assigned to another net member whenthe request is received. The process of granting and denyingtransmission requests is known as arbitration. Other arbitration schemesevaluate factors such as priority levels assigned to each CD indetermining whether a requesting net member is granted the transmissionprivilege.

In order to participate in the NBS system 10, CDs 12, 14, 16, and 17each have the ability to request transmission privilege from acontroller or a communications manager (CM) 18. CM 18 generally managesthe real-time and administrative operation of nets. The CM is any typeof computer type device having at least one processor and memory. In anembodiment, the CM is a Sun Workstation Netra T1™.

The CM 18 maintains a list of defined nets, defined as either clear orsecure. Transitions between clear and secure are generally notpermitted. A secure net relies on encryption provided by the individualCDs to provide authentication and guard against eavesdropping.Encryption for secure nets is implemented on an end-to-end basis,meaning that encryption and decryption takes place within each CD. TheCM 18 generally operates without knowledge of security algorithms, keys,or policies.

The CM 18 manages remotely through either a communication system serviceprovider, net members, or both, assuming that authorization is providedby the service provider. The CM 18 may receive net definitions throughan external administration interface. Net members may requestadministrative actions through their service provider or administratenet functions through defined systems, such as a member-operatedsecurity manager (SM) 20 that conforms to a CM 18 administrationinterface. The CM 18 can authenticate to high-grade commercial standardsany party attempting to establish or modify a net.

The SM 20 is an optional component of the NBS system 10 that performskey management, user authentication, and related tasks to support securenets. A single group communication system may interact with one or moreSM 20. The SM 20 is generally not involved in the real-time control of anet, including net activation or PTT arbitration. The SM 20 may haveadministration capabilities compatible with a CM 18 interface toautomate administration functions. The SM 20 may also be capable ofacting as a data endpoint for the purpose of participating in a net,broadcast net keys, or simply monitor net traffic.

In one embodiment, the means for requesting the transmission privilegefrom a CD comprises a push-to-talk (PTT) key or switch. When a user inthe NBS 10 desires to transmit information to other net members, thepush-to-talk switch located on his or her CD is depressed, sending arequest to obtain the transmission privilege from the CM 18. If no othernet member is currently assigned the transmission privilege, therequesting user is granted the transmission privilege and is notified byan audible, visual, or tactile alert through the CD. After therequesting user has been granted the transmission privilege, informationmay be then transmitted from that user to the other net member.

In one embodiment of the present invention, each wireless net memberestablishes a forward link and a reverse link with one or more basestations 22 or a satellite gateway 24, as the case may be. The basestation 22 is used to describe a communication channel from the basestation 22 or the satellite gateway 24 to a CD. The satellite gateway 24is used to describe a communication channel from a CD to a base station22 or gateway 24. Voice and/or data is converted into data packets usinga CD, the data packets suitable for a particular distributed network 26through which communications to other users take place. In oneembodiment, distributed network 26 is the Internet. In anotherembodiment, a dedicated forward channel is established in eachcommunication system (i.e.,a terrestrial communication system and asatellite communication system) for broadcasting information from eachnet member to the other net members. Each net member receivescommunications from other net members over the dedicated channel. In yetanother embodiment, a dedicated reverse link is established in eachcommunication system for transmitting information to the CM 18. Finally,a combination of the above schemes may be used. For instance, a schememay be establishing a dedicated forward broadcast channel but requiringwireless CDs to transmit information to the CM 18 over an individualreverse link assigned to each CD.

When a first net member wishes to transmit information to other membersof the net, the first net member requests the transmission privilege bypressing a push-to-talk key on his or her CD, which generates a requestformatted for transmission over the distributed network 26. In the caseof CDs 12, 14 and 16, the request is transmitted over-the-air to one ormore base stations 22. A mobile switching center (MSC) 28 comprises awell-known inter-working function (IWF) for processing data packets,including the request, between the MSC 28 and the distributed network26. For CD 16, the request is transmitted via satellite to satellitegateway 24. For the CD 17, the request is transmitted to the PublicSwitched Telephone Network (PSTN) 30, then to a modem bank 32. Modembank 32 receives the request and provides it to the distributed network26. A NBS terminal 34 monitors traffic of the NBS system through itsconnection to the Internet 26. Since the NBS terminal 34 is connected tothe Internet 26, geographic proximity to net participants is notnecessary.

If no other member currently holds the transmission privilege when thetransmission privilege request is received by CM 18, CM 18 transmits amessage to the requesting net member, notifying it that the transmissionprivilege has been granted. Audio, visual, or other information from thefirst net member may then be transmitted to the other net members bysending the information to CM 18, using one of the just-describedtransmission paths. In one embodiment, CM 18 then provides theinformation to the net members by duplicating the information andsending each duplicate to the net members. If a single broadcast channelis used, the information need only be duplicated once for each broadcastchannel in use.

In an alternative embodiment, CM 18 is incorporated into MSC 28 so thatdata packets from supporting base stations are routed directly to CM 18without being routed onto distributed network 26. In this embodiment, CM18 is still connected to distributed network 26 so that othercommunication systems and devices can participate in a groupcommunication.

CM 18 maintains one or more databases for managing informationpertaining to individual net members as well as to each defined net. Forexample, for each net member, a database may comprise information suchas the user name, account number, a telephone number, or dial number,associated with the member's CD, a Mobile Identification Number assignedto the CD, the current member's status in the net, such as whether themember is actively participating in the net, a priority code fordetermining how the transmission privilege is assigned, a data telephonenumber associated with the CD, an IP address associated with the CD, andan indication of which nets the member is authorized to communicate.Other related types of information may also be stored by the databasewith respect to each net member.

As part of the NBS infrastructure, the communications manager (CM) formsconnections of individual communication terminals to form one talkgroup, or net. The CM comprises a variety of functional capabilities inhardware and software that are configurable in different ways toaccommodate different applications. Generally, the CM providescapability to manage real-time, administrative, and authenticityoperations of (NBS) nets, push-to-talk (PTT) request arbitration,maintenance and distribution of net membership and registration lists,call set-up and tear-down of necessary CDMA system and networkresources, as well as overall control of net status.

The NBS net may be within a stand-alone deployable cellular system, or alarge multiple site configuration. In the case of a large configuration,multiple CMs may be deployed geographically to form a single, integratedsystem, each operates as a plug-in module into existing cellularinfrastructure. As such, new features introduced by NBS nets areavailable to cellular users without requiring modification to existingcellular infrastructure.

A function of the CM is to maintain a list of defined NBS nets. Each netdefinition includes a net identifier, a list of members, including phonenumbers or other identifying information, user priority information, andother generic administration information. Nets are statically defined aseither clear or secure, and transitions between clear and secure are notpermitted. A secure NBS net typically uses media encryption to provideauthentication and guard against eavesdropping. Media encryption forsecure nets is implemented on an end-to-end basis, meaning encryptionand decryption takes place within the communication device. The CMoperates without knowledge of security algorithms, keys, or policies.

The CM receives net definitions through an external administrationinterface. Customers may request administrative actions through itsservice provider or administrate net functions through defined systems,such as a customer-operated security manager that conforms to the CMadministration interface. The CM authenticates to high-grade commercialstandards for any party attempting to establish or modify a net.

Before one embodiment of the invention is explained in detail, it is tobe understood that the invention is not limited in its application tothe details of the construction and the arrangement of the componentsset forth in the following description or illustrated in the drawings.The invention is capable of other embodiments and are carried out invarious ways. Also, it is understood that the phraseology andterminology used herein is for purpose of description and should not beregarded as limiting.

FIG. 2 illustrates a NBS net 100 and how communication devices interactwith a CM 104. Multiple CMs 104 may be deployed as desired forlarge-scale NBS nets 100. In FIG. 2, communication device 108, or a CD108, has permission to transmit media onto the net. In this case, the CD108 is known as the talker, and transmits media over a channel. When theCD 108 is designated as the talker, the remaining net participants,communication devices 112 and 116 (or CD 112 and CD 116) do not havepermission to transmit media to the net. Accordingly, CD 112 and CD 116are designated as listeners. If CD 116 is designated as the talker, CD108 and CD 112 are designated as listeners, and so on.

As described above, each CD 108, 112 and 116 is connected to the CM 104using at least one channel. In an embodiment, the channel is dividedinto separate channels comprising a session initiation protocol (SIP)channel 120, a NBS media signaling channel 124, and a media trafficchannel 128. The session initiation protocol (SIP) channel 120 and theNBS media signaling channel 124 may be used at any time as bandwidthallows, regardless of being designated a talker or a listener, by any ofthe CD's 108, 112 and 116. The SIP is an Internet Engineering Task Force(IETF) defined application-layer protocol that describes controlmechanisms to establish, modify, and terminate multimedia sessionsoperating over Internet Protocol (IP). SIP provides a general solutionto call-signaling problems for Internet telephony applications bysupporting means to register and locate users, mechanism that defineuser capabilities and describe media parameters, mechanisms to determineuser availability, call setup, and call-handling.

The SIP channel 120 is used to start and end participation of a CDwithin the net 100. Optionally, a session description protocol (SDP)signal may also be used within the SIP channel 120. When the CD'sparticipation within an NBS net is setup using the SIP channel 120,real-time call control and signaling between the CD and the CM 104 takesplace using the NBS media signaling channel 124. Specifically, amongother tasks, the NBS media signaling channel 124 is used for handlingpush-to-talk requests and releases, arbitrate between conflictingrequests, or floor control, announce the beginning and end ofinformation transmission, manage net dormancy, track endpointconnectivity, request and exchange net status, notification and errormessages. The protocol of the NBS media signaling channel 124 minimizesthe length of the most common messages, and to simplify the task ofinterpreting replies and responding to requests while retainingflexibility for future enhancements. The protocol of the NBS mediasignaling channel 124 also allows requests to be resent withoutadversely affecting protocol state.

Signaling traffic on the media channel 124 may further be differentiatedinto two categories: call setup and control signaling, which consistsprimarily of SIP invitation requests and acknowledgements, and mediasignaling, which is comprised primarily of real-time floor controlrequests and related asynchronous messages. Media traffic on the mediatraffic channel 128 is comprised of real-time point-to-multi-point voiceand/or data broadcasts. Both messaging categories have unique functionalattributes. In addition, each CD may issue Domain Name Service (DNS)client requests to facilitate mapping fully-qualified DNS hostnames toInternet network addresses.

NBS call setup and call control signaling is performed according to SIPsemantics. Although SIP may be transported using either the well knownUser Datagram Protocol (UDP) or Transmission Control Protocol (TCP), ina preferred embodiment, each CD performs SIP based signaling functionsusing UDP, as illustrated in FIG. 4. Also, each CM expects to receiveall SIP signaling requests via UDP. Real-time signaling occurs viadynamic UDP/IP interfaces on the CM and each CD. Other signaling maytake place via a fixed TCP/IP interface between the CM and the CD usingthe SIP.

FIG. 3 illustrates the modules and physical make-up of the CM 200. TheCM 200 comprises of a CM core module or complex 204, at least one netmodule, or media control unit (MCU) 208 and 212, a DNS server 216, aredirect server 220 and an administration workstation 224. The CM corecomplex 204 provides administration capability to a Java™-capableweb-browser. One or more DNS servers 216 may also be included in the CMcore complex 204. The CM core complex 204 further comprises a CM node228 and a database server 232. The CM 200 is separable into at least twoparts, the CM core complex 204 and each MCU node 208. After initialconnection into the CM core complex 204, a net is operated by MCU node208. The MCU node 208 sends and receives information as necessary fromthe CM core complex 204. The separability of the CM core complex 204allows for versatility in that once a particular net is established, thenet is operated by a dedicated MCU node 208. This allows CM core complex204 to provide initial connections with other potential nets,irrespective of the type of communication structure in which the netwishes to operate. Also, the CM core complex 204 may be geographicallydisplaced from the MCU node 208. For example, a single CM core complex204 may be located in the central part of the United States, and aplurality of MCU nodes 208 may be located regionally to operate netsfrom its given region. As such, the CM core complex 204 may route a userto a particular MCU node 208 based on the location of the user. Also,information may be provided to a user or group of users based onlocation, such as location-based broadcasting, directions, oridentification of landmarks.

The CM node 228 provides centralized functionality associated with NBSnets. The CM node 228 comprises a session initiation protocol user agentserver (SIP UAS) server 236, and CM manager 240, a central billing log244, and an administration server 248. The SIP UAS server 236 supportsuser requests for net lists and handles SIP invite messages for nets.When a SIP invite message is received from a communication device, thenet assigns the communication device to an appropriate MCU node 208, anddirects the communication device to the MCU node 208.

The CM manager 240 monitors the status of all the MCU nodes within anet, and assigns the execution of nets to given MCU nodes, such as theMCU node 208. The CM manager 240 handles administrative functionspertaining to net administration, including the creation and deletion ofnets, defining new and deleting existing users, adding and removingusers as net members, and adjusting various operating parameters at auser, net, or CM wide basis.

The central billing log 244 maintains time and identificationinformation for billing purposes. The central billing log receivesbilling log information from a local log server 260 of the MCU node 208.Detailed log information of each user, such as which communicationdevices are active on the net, for how long, from where, and when andfor how long each CD is a talker or a listener, is maintained. TheAdministration Server 248 supports an interface to allow theAdministration workstation 224 to retrieve status information, initiatedatabase administration and system management functions through the netstatus interface.

The CM implements both the SIP user-agent server 236 and a SIP MCUserver 252. To support NBS, each CD implements a SIP user-agent client.The CM receives incoming SIP connections on an advertised node, or port.When a connection occurs, the SIP server 236 receives and processesrequests according to SIP call-signaling conventions. The SIP server 236is capable of processing multiple call-signaling connections inparallel.

To conserve network resources, the CD may release its UDP connectionwith the SIP server 236 after it has successfully (or unsuccessfully)joined the NBS net 100. The UDP connection may be reinstated later tosend additional SIP call-signaling requests (for example, to leave thenet or switch to another net).

FIG. 4 illustrates an example of a NBS SIP signaling protocol stack 300.The stack is a collection of protocol layers that implements networkcommunication. The protocol associated with each layer communicates withthe layers immediately above and below it, and assumes the support ofunderlying layers. Because UDP is a less reliable connectionlesstransport, application level reliability is preferable to insure robustcommunication, which is achieved by implementing by SIP compliantendpoints. Generally, SIP call-signaling 302 on UDP streams 304 areencapsulated within IP protocol 306. No special formatting is required.SIP call-signaling IP packets 306 are exchanged between, for example, aCDMA cellular based CD or a dial-up PSTN based CD, which areencapsulated within point-to-point protocol (PPP) frames 308.Accordingly, no special formatting is required. Also, SIP call-signalingPPP frames 308 exchanged between a CDMA cellular based CD and a basestation are encapsulated within a radio link protocol (RLP) 310. Fordial-up PSTN based users, an appropriate modem standard, such as V.32bisor V.90, may replace RLP 310. In either case, special treatment isgenerally not required and an error-free physical link is not assumed.

FIG. 5 illustrates an NBS media signaling protocol stack 312,transporting voice and data traffic using UDP datagrams 304 over IP 306.NBS media signaling 314 is layered onto UDP/IP traffic, and is handledin a similar manner with respect to the description of FIG. 4.

FIG. 6 illustrates a real-time voice-media protocol stack 320. In thisembodiment, vocoder payload data 322 is layered on real time protocol(RTP) 324. RTP 324 is then layered onto UDP 304 and IP 306. In anoptional embodiment, compressed real time protocol (CRTP) headercompression 330 is used to further encapsulate media traffic using RTP324 at the application layer. Header compression techniques may beapplied as appropriate to all UDP/IP incoming and outgoing UDP/IPtraffic illustrated in FIGS. 4–9. Media signaling requests and responsesare encapsulated within UDP datagrams. When available, CRTP headercompression may be applied to reduce the impact of sending uncompressedUDP/IP headers. In FIG. 6, CRTP compresses RTP layer 324, UDP layer 304,IP layer 306 and the PPP layer 308. In FIGS. 4, 5 and 7–9, CRTP 320compresses the layers between and including UDP 304 to PPP 308.

In operation, each CD dynamically selects a UDP port on which it intendsto listen for NBS media signaling requests and communicates the portnumber to the SIP server 236 as part of the SIP invitation it deliverswhen attempting to join a net. The net's CM media signaling destinationaddress (including the UDP port number) is described in the net'ssession description delivered as part of a successful SIP INVITErequest's response to the CD. Unlike SIP signaling addresses, mediasignaling destination addresses are net specific and may change betweeninstances of a CD joining a net. Multiple nets hosted by the same CMgenerally operate independently and do not share media signaling ormedia traffic ports. However, it is contemplated that multiple nets mayshare media signaling and media traffic ports.

Referring to FIG. 6, voice traffic is encapsulated by grouping one ormore vocoder frames within an RTPJUDP 324 or UDP payload 304. The use ofRTP 324 with CRTP 330 enabled is used to minimize end-to-end medialatency and provide interoperability with IP telephony applications andservices. In either case, the CD dynamically selects the UDP port onwhich it expects to receive media traffic and communicates the portnumber to the SIP server 236 as part of the SIP invitation it deliverswhen attempting to join a net.

The net's vocoder and transport encapsulation protocol, as well as itsmedia traffic destination address (including the UDP port number), isdescribed in the session description response to a successful SIPinvitation request from the SIP server 236. Like a net's media signalingaddresses, the media traffic destination addresses are net specific andmay change between instances of a CD joining a net.

Typically, as shown in FIG. 6, voice traffic is encapsulated at theapplication layer using RTP 324, which segments each UDP datagram 304into a RTP header 324 and vocoder payload 322. FIG. 7 illustrates a UDPvoice media protocol stack 332. Voice traffic may optionally beencapsulated purely using UDP datagrams 304, with no RTP encapsulation,typically when CRTP header compression 330 is unavailable or unsupportedby a net member. FIG. 8 illustrates a media traffic protocol stack 334.The media traffic protocol stack 334 is used for net participants withno application-level RTP encapsulation. Data 336 is encapsulated intoUDP datagrams 304.

The structure of the UDP payload 304 follows the definition given for acorresponding RTP payload 324, without the RTP header fields. Thedecision to encapsulate media directly into UDP 304 is configured by thenet's administrator 248 and advertised by the net's sessionannouncement. In addition to voice media, NBS nets may also supportarbitrary data broadcasts. If a net supports a data broadcast channel,the SIP server 236 advertises the media type in the net's SIP sessiondescription when a CD formally joins the net.

FIG. 9 illustrates a DNS client protocol stack 338. Each CD includes thecapability to resolve Internet domain names into Internet addressesusing a Domain Name Service (DNS) protocol 340. The CD operates as a DNSclient. The CD encapsulates DNS 340 requests using UDP 304, as shown inFIG. 9. In order for the CD to resolve DNS hostnames, the CD isprovisioned with the IP network address of the DNS server 216, as shownin FIG. 3. The DNS address is also configurable by the CD serviceprovider and, optionally, by the user.

In addition to voice media, nets may also support arbitrary databroadcasts, such as secure net rekey, email, data files, etc. If a netsupports a data broadcast channel, the CM advertises the media type inthe net's SIP session description when the CD formally joins the net.Like traditional media broadcasts, generic data broadcasts operate overRLP in one embodiment (or a corresponding physical layer) but aregenerally considered less reliable transports.

The CD includes the capability to resolve Internet domain names intoInternet addresses using the Domain Name Service (DNS) protocol, asdefined in RFC 1034. Alternatively, the CD operates as a DNS client orresolver, as described in RFC 1035.

In order for the CD to resolve DNS hostnames, the CD is preprogrammedwith the IP network address of a DNS server. The DNS address is alsoconfigurable by the CD service provider and, optionally, by the user.

The CM 104 may optionally be configured to act as a DNS server 216.Although it may respond to DNS requests from foreign entities using TCPas the transport protocol, for the purpose of servicing requestsoriginating with the CD, the SIP server 236 also encapsulates DNSmessages using the UDP 304 according to FIG. 8.

The NBS also takes advantage of the development of a cellular multicastchannel. Such a channel generically allows one transmitting station toaddress N listening stations directly over one forward channel, withoutthe need for N separate rebroadcasts of the transmitted data. Thepresence of a cellular multicast channel implies changes to the NBSmedia stack primarily below the IP network layer. To take advantage ofthe efficiencies provided by a cellular multicast channel, a net's mediasignaling and traffic destination addresses are conventional IPmulticast channels, and CM originated media signaling and trafficbroadcasts are multicast broadcasts. Each CD originated media signalingand traffic broadcasts and SIP signaling remain as point-to-pointcommunications.

The Radio Link Protocol (RLP) 310 shown in FIGS. 4–9 may be modifiedwithin each CD to minimize the latency experienced when link-layer (RLPframe) loss occurs. Such modifications are optional and do notnecessarily affect the operation of transport of application layerprotocols, since neither TCP nor UDP 304 assumes a reliable network (IP)or link-layer service.

A variety of the RLP 310 modification strategies are possible. Forexample, the RLP 310 may be modified to send multiple messages, such asNAK responses, after an initial RLP timeout, thus prompting the remoteend to transmit multiple copies of the lost RLP 310 frame and improvingthe chances of a successful the RLP 310 recovery. The RLP 310 may alsobe modified to never send a NAK responses (after the RLP timeoutexpires) and allow dropped RLP 310 frames to force higher levels of theprotocol stack to generate errors. Any application level protocols basedon TCP recover routinely using TCP's error recovery mechanisms. Trafficrelying on the UDP 304 for transport already contends with the potentialfor loss.

Referring back to FIG. 2, once the CD establishes participation withinthe NBS net 100 using the SIP channel 120, the CD is prepared to sendand receive media from the net 100 on a specific media port of the CDover the media traffic channel 128. If the CD gains control of the floorthrough media signaling, as the case with CD 108 of FIG. 2, the CDtransmits media to the destination network and transport addresses asindicated in the session description of the net 100. The CD decodesmedia received on its media ports according to the vocoder and mediaformat defined in the session description of the net 100 received in aninvite response when the CD joined the net 100. The CD codes andencapsulates media sent to the net 100 according to the vocoder andmedia format defined in the session description of the net 100 receivedin an invite response when the CD joined the net 100.

Each CD participating in a net determines the destination network andtransport address for each media channel from the session descriptionreceived from the SIP server 236 of the CM 104 and acknowledged duringthe SIP call set-up and use it to address corresponding media sentwithin the net 100. Each CD provides a packet data connection to the CM.Changes in the CD implementation of this interface may be made tooptimize NBS performance. Changes to the infrastructure side of thisinterface are generally not necessary. The CD may optionally supportmost NBS activities using Quick Net Connect (QNC), as further describedherein.

Upon delivery to a service provider, the CM manager 240 goes throughbasic administrative configuration before supporting NBS activities.Initial configuration involves basic system configuration such asassigning passwords to operating system level accounts for root-levelsystem administration and configuring CM manager 240 network interfacesfor proper operation on the local wireless infrastructure network.

Once the CM 104 is configured, general net administration can takeplace. Net administration functions take place through an HTML or othernetwork interface built over TCP/IP. The administration workstation 224interacts with the CM core complex 204 using a conventional World WideWeb (WWW) browser. Administration can take place locally or remotely(anywhere on the Internet, or via dial-up). However, the underlyingtransport path for administrative access is typically TCP/IP. Also,multiple (at least three) simultaneous administration connections areallowed.

Upon connecting to the CM core complex 204 for the purpose of netadministration, the administrator workstation 224 successfullyauthenticates itself to insure that only authorized administrativeactions are accepted. Different levels of access are accommodated; forexample, authorized net members may connect directly to the CM'sadministrative interface 248 to modify specific net membership lists.More generic administrative privileges are generally reserved forspecific administrative accounts. For clarity, administrative actionsare generally separated into those that deal specifically with userdefinitions and those that define nets. A user definition comprisesinformation such as the username, unique CD cellular system identifier,CD phone number, and user e-mail address. A unique user identifier isdefined that may be passed to the CD and used to uniquely identify theuser in signaling messages. A net definition comprises information suchas the net-address, net hang-time, private dispatch timeout, and memberlist. A net's member list comprises of information such as of a list ofmember records, which individually contain a user identifier andpriority level. A member with the minimal level of priority typicallyhas listen-only privileges.

The CM administrator 248 may monitor the current status of nets forwhich they have administrative privileges. In particular, the CMadministrator 248 may determine the current list of net participants, aswell as monitor the net's state (active, inactive, dormant, in wake-up,etc.). Whenever the net is active, the CM administrator 248 may alsomonitor the identity of the current talker. Additional statistics andstatus, such as the length of current session, total talk time, meannumber of registrants, etc., may also be available to administratorsthrough the administrative interface.

The administration server 248 interface comprises of at least twonetwork nodes, or ports. One is a TCP/IP based Hyper Text TransferProtocol (HTTP) interface supporting administrative access through aconventional Java™-capable web browser. The second is a TCP/IP based NBSspecific Command Lime Interface (CLI).

The administration server 248 makes all administrative functionsavailable to a generic web browser via a HTTP web server interface withone or more pages formatted using an Internet readable medium, such asHyper Text Markup Language (HTML) syntax. At least one of theadministrative pages may include a reference to an embedded Java™applet. Some administrative functions may optionally be performedthrough ITTP GET and POST commands issued by the web browser usingconventional HTACCESS authorization mechanisms. The administrativefunctions supported are generally a subset of those supported by the CLIinterface.

The HTTP interface may be used to deliver a Java™ applet to the webbrowser. The applet may then rely on the administrative server 248 CLIinterface to provide additional administrative functionality to the userthrough a web browser interface. Prior to being granted access to theCLI interface, a potential administration workstation 224 connecting tothe administrative server 248 CLI interface is authenticated. In apreferred embodiment, the CLI interface is reachable on a well-known,fixed, TCP port address and is able to simultaneously manage multipleCLI sessions.

The data base server 232 is responsible for storage of net informationand parameters, net user information, status information associated withthe MCUs 208 and 212, and the CM node 228. The database server 232 alsoserves this information to the remainder of the CM 104, such as the SIPserver 236 and other modules that need such information. The databaseserver 232 maintains databases that capture information that support NBSnet activities, including an NBS net database portion and an NBS userdatabase portion. Information supporting administration activities andprivileges may be stored in either database, or a third functionallydistinct database. The database server may be further subdivided into auser portion and a net portion.

The CLI interface supports administrative functions such as CLI createuser/net, delete user/net, modify user/net, list/show user, list/shownet, status and help. The Create User function allows the administrationserver 248 to create new users in the user portion of the database,including specifying all user record fields. The Delete User functionallows the administration server 248 to delete existing user records inthe user portion of the database 232. The Modify User function allowsthe administration server 248 to modify existing user records in theuser portion of the database 232, including modifying all record fieldsfor a specific user.

The Create Net function allows the administration server 248 to createnew nets in the user portion of the database 232, including specifyingall net definition parameters. The Delete Net function allows theadministration server 248 to delete existing nets in the user portion ofthe database 232. The Modify Net function allows the administrationserver 248 to modify existing nets in the user portion of the database232, including modifying all net definition parameters for a specificnet. The List User function allows the administration server 248 to listall users, by user name, dial number, and user identifier, in the userportion of the database 232.

The List Net function allows the administration server 248 to list allnets, by net-address and net identifier, in the net portion of thedatabase 232. The Show User function allows the administration server248 to show all fields for a specific user identified by the user's useridentifier. The Show Net function allows the administration server 248to show all fields for a specific net identified by the net's netidentifier or net address. The Status function allows the administrationserver 248 to query for a static status report for a specific net. TheStatus function may also allow the administration server 248 to queryfor real-time (updated) reports. In particular, the status functionidentifies the current list of net participants, the current talker, thepresence or absence of media traffic, and identifies any and all mediasignaling messages sent or received by the CM. The Help function allowsthe administration server 248 to query for a brief human-readablesummary of each supported CLI command, including usage and syntaxdescription.

The NBS user portion of the database 232 tracks individual users of NBS.The user records contained within the database 232 may or may notnecessarily be members of net's defined in the CM's net portion of thedatabase 232.

Each record in the user portion of the database 232 is comprised offields such as user name, user identification, vocoder list, dialnumber, user type, CRTP support, CD user address, and CD pretty goodprivacy (PGP) public key. The vocoder list is a list of vocoderssupported by the subscriber's CD. The list may include vocoders notsupported by NBS. The dial number is the dial number of the subscriber'sCD. This field is empty, or null, for generic Internet users. The usertype is a type field describing whether the user is a CDMA cellular orgeneric Internet user. Users who connect via PSTN dial-up are consideredgeneric Internet users. The CRTP support is a flag indicating whetherthe CD supports and attempts to negotiate CRTP Header Compression overPPP when connecting. This flag is valid for cellular as well as PSTNbased users. The CD user address is the globally unique user address forthe CD. A CD known by multiple user addresses will have multiplecorresponding entries in the user portion of the database 232. The PGPpublic key is the key associated with the CD user address.

The NBS net database defines the set of nets known to the CM. The netportion of the database 232 also lists the defined members of each net;that is, those users who may request to join and become participants ina net. Each record in the net portion of the database 232 is comprisedof a variety of fields. Fields include a net identifier, which is aunique integer identifying the net within the context of the CM. Fieldsalso include a net-address, which is the SEP compatible net-address ofthe net. Net owner(s), a non-empty list of users, is identified by useridentifiers who have administrative privileges (defined separately) forthe net. Also, net security status is a field for a flag indicatingwhether the net is clear or secure.

Fields also include arbitration scheme, which is a unique valueidentifying the arbitration scheme used to resolve PTT arbitrationconflicts between net participants. Net vocoder describes a field havinga unique value identifying the standard vocoder shown in the net'sadvertised session description. Defined members of the net have thisvocoder listed in their list of supported vocoders. PTT fail-safetimeout is the maximum number of seconds a net participant may transmitmedia to the net before the CM revokes control of the floor with a PTXdenial message. Hang-time timeout value is the maximum number of secondsthe net may remain idle before the CM will place it in the dormantstate. PTX Dormancy Response timeout value is the maximum number ofseconds the CM waits after determining that a dormant net's floor can begranted before transmitting the PTX grant response to the requesting CD.Wake-up timeout value is the maximum number of seconds the CM waits fornet participants to respond to the AYT “wake-up” message before grantingan outstanding PTT request. Late-riser timeout value is the maximumnumber of seconds the CM waits for a CD to respond to the CM's AYT“wake-up” message before the CM will remove the non-responding CD fromthe net's list of active participants. AYT timeout value is the maximumnumber of seconds the CM waits for a CD to respond to a CM's AYT messagebefore the CM removes the CD from the net's list of active participants.Media channels list is a list of media channels, including payloadspecifications, for the net (nets list at least one media channel, whichtransports voice).

The net membership list defines the set of users who may request to jointhe net as participants and associated net specific privileges. Eachentry in the list contains fields such as the user identifier, which isa unique identifier of a user listed in the CM's user database 232.Fields also include the user net priority level, which is the user'spriority level to be used by the net's PTT arbitration algorithm inresolving PTT conflicts. A priority level of zero indicates that theuser has listen-only privileges and may never be granted control of thenet. Fields may also include a user authorization list, which detailsthe authorization privileges, if any, the user has for the net.Privileges may include the ability to add, edit, or modify entries inthe net's membership list and the ability to modify other netparameters.

Each CD maintains a database, also known as the group-list, identifyingknown nets that the CD may request to join. Each entry in the CDdatabase includes fields such as net address, net security advisoryflag, net traffic encryption key, and dormancy baby-sit timer. The netaddress is the net's formal SIP net-address that the CD uses to requestto join the net as an active participant. The Net security advisory flagis the clear/secure advisory flag distributed by the CM's SIP server 236in its list of available nets or set by the user to indicate that a netdefined to carry Type IV secure media traffic. The net trafficencryption key is the traffic encryption key used to encrypt and decryptall media traffic for Type IV secure nets. The dormancy baby-sit timeris the length of the interval, in seconds, the CD will wait when in theDormant/Idle state between transitioning to the Connected state,confirming that the packet data call remains valid and the base stationhas not unilaterally dropped the connection.

The MCU node 208 comprises of an MCU 252, a MCU node manager 256 and thelocal log server 260. The MCU node 208 and 212 may also optionallycomprise of an additional MCU 264. The MCU node 212 is substantially thesame as the MCU node 208. For description purposes, only the MCU node208 is discussed herein. The MCU 252 is responsible for control of asingle active net. The MCU supports SIP, media signaling, and mediainterfaces for the net, and provides the functionality associated withthe normal operation of the net. Each MCU node 208 may have a pool ofMCUs 252 that may be directed to manage nets as appropriate. Each MCU252 provides a MCU management interface to support functions such asstarting, stopping, and status reporting.

The MCU node manager 256 monitors the operation of the MCU node 208 andmanages the operation of each MCU 252 on its MCU node 256. The MCU nodemanager 256 also provides an external interface to the CM core complex204 to allow for startup and/or shutdown, assigning a net to the node,and sharing of status information. The local log server 260 locallyrecords all log events for the MCU node 208. The local log server 260also responds to requests from the central log server 244 via its logevents interface. Requests include uploading certain event classes orpriorities. In order to prevent loss of events, the messages are storedin the local log server 260 until an acknowledgement is received by thecentral billing log server 244.

The DNS server 216 provides name services to the NBS communicationdevices. The DNS server 216 may service SRV record requests. The DNSserver 216 may be located anywhere on the network. In an embodiment, theDNS server 216 is a part of the CM core complex 204.

Each CD maintains a list of nets, or a group-list, internallyrepresenting the set of known nets in which the CD can participate. Thelist is non-volatile, but may be updated as needed either throughinteractions with a CM 104 or interactively by the user. The user isalso able to determine who and how many users are either active orinactive in the net. The NBS group-list maintained internally by a CD isanalogous in function to the list of names and dial-numbers maintainedin the phonebook and used to facilitate voice-services. The NBS grouplist may be integrated with the phone's conventional phone book. Ineither case, the act of selecting a net from the group list instructsthe phone to attempt to join the selected net.

In order to participate in a specific NBS net, each CD initiallyrequests that the CM add itself to the list of active net participantsfor a specific net. Thus, each CD initially is aware or is able to learnthe net-address of any nets in which it wishes to participate. Further,each CD initially knows or is able to be configured with the address ofa top-level SIP server 236 to which SIP requests may be sent.

Net addresses may be provisioned or learned by a CD in several differentways. For example, in an embodiment the CD may be initially provisionedwith the address of a known or default top-level SIP server 236 thatprovides a current list of nets in which the CD can participate. The CDmay also be provisioned with a group-list, which defines at least onenet-address in which the CD is a member. The CD may later send a requestto the top-level SIP server 236 to update its group-list. In the eventthat no explicit NBS provisioning has taken place for the CD, the usermay be provided with a top-level SIP server 236 and net address tointeractively enter into the CD before using NBS. The user may alsointeractively enter additional net-addresses to a group-list that hasalready been provisioned with entries. Such a configuration step isanalogous to entering personal names and dial-numbers into theconventional phone-book.

Note that although users may interactively enter a net-address into theCD group-list, the corresponding net and top-level SIP server 236 arepreferably in existence and the user is needed to be listed as a memberof the net in order for the CD to be able to successfully participate inthe net.

The CD may also be provisioned with the IP network address of theprimary Domain Name Service (DNS) server 216, to which the CD can sendDNS queries. Typically, the address of the DNS server 216 operated by aCDMA cellular carrier is provisioned. The CD may also be provisionedwith the IP network address of an alternate DNS server.

In order to support SIP authentication, the CD may be provisioned with aunique PGP user-id and secret key that it can use to sign SIPtransactions when requested by the CM 104. The PGP user-id may also beused as the CD user address for generic SIP transactions.

FIG. 10 illustrates the high level functionality of the group servicesmodule 500 of the CD. Normally, the group services module is initializedto a default idle state 504 when the CD is powered on. From the idlestate 504, the CD may transition to other states that allow it toactively participate in NBS nets.

The user may wish to temporarily disable NBS services through a menuoption within the CD user-interface. If the user has disabled NBSservices, the group services module defaults to a disabled state 508when the CD is powered on. When disabled, the CD does not attempt toautomatically join in any NBS nets. Further, the CD does not perform anyNBS specific SIP transactions (the CD may maintain registrations orperform other SIP transactions for other IP based telephony applicationsresiding within the CD).

Optionally, group services may be hidden entirely from the user byprovisioning group services within the CD to an unequipped state 512.The unequipped state disables group services, where an equipped stateenables group services. Once unequipped, the CD requires administrativeprovisioning to equip group services. When group services areunequipped, the NBS group services functionality and related userinterface features are not available to the user.

The CD may support over-the-air provisioning to equip NBS groupservices. In the event that the group-list of the CD contains more thanone net-address, no more than one net-address may be identified as adefault net 514. If a net-address is selected, the CD attempts toautomatically transition from the idle state 504 by attempting to jointhis selected net shortly after the CD is powered on.

When the CD is connected, the CD cycles from a quiet state 516, a listenstate 520, a talk state 524 and a dormant state 528 based on where theuser is in the push-to-talk system as described with respect to FIG. 16.

The NBS relies on call signaling syntax and semantics as defined by theSIP to advertise available net-addresses and provide mechanisms by whichan individual CD can formally join or leave nets. The CM 104, along withother functional entities, includes the a top-level SIP server 236, oneor more multipoint control units (MCUs) 252 and associated SIPuser-agent servers, and user and net portions of the administrationdatabase 232. The top-level SIP server 236 acts as a known rendezvouspoint to participate in the system. Each MCU 252 performs mediasignaling and media traffic switching for one or more nets. The database232 stores and provides known user, administration, and net-addressdefinitions and may serve multiple CM installations or be accessedremotely.

Each CD is provisioned with a list of net-addresses, and one or moretop-level SIP server 236 addresses. If the group-list is empty, the usermay interactively specify the address of an existing net. If notop-level SIP server 236 is defined, the user may interactively specifythe address of a top-level SIP server 236. Once the top-level SIP server236 address is known, the CD may request an updated list of netsavailable to it by placing a call using the SIP INVITE method to apre-defined SIP destination.

The top-level SIP server 236 may redirect the request to an internaldestination or respond to it directly. The INVITE response to this callincludes the current list of nets available to the CD. The CD uses thislist to update its internal group-list.

After a net has been selected, the CD attempts to join the net using theSIP INVITE method by specifying the net-address as the invitationdestination and sending the request to the top-level SIP server 236. Thetop-level server 236 attempts to map the net-address to a knowndestination and, if successful, redirects the CD to the correspondingSIP user-agent server of the MCU 252. If no mapping is available, theinvitation generally fails.

Normally, the destination SIP user-agent server of the MCU 252 confirmsthat the CD is a member of the selected net and responds to theinvitation, embedding a description of the media traffic and signalingparameters to use to participate in the net in the content of itsresponse. The SIP user-agent server of the MCU 252 may also reply withan error if it is unable to confirm the CD as a legitimate member of thenet or if some other error condition arises, such as a failure thatprecludes normal net operation. If the invitation is accepted, the CDacknowledges the response through a message, such as the SIP ACK method.Note that other transient response codes that indicate call progress mayalso be received by the CD while the invitation is being processed.

The CD is responsible for updating its group-list to the set of the netsin which it may participate. The user may command the CD to query thedatabase 232 of the CM 104, even when no net-address is selected, forthe purpose of receiving updates to its group-list. If the CD determinesthat it has been added or removed from a net, it briefly displays anappropriate message to the user (for example: “Added to group X”) and/orpossibly prompt for user interaction. If the CD determines that is not amember of any net, it will similarly inform the user. The CD mayautomatically incorporate new net addresses into its group-list but mayprompt the user before deleting addresses of nets in which it has lostmembership from the group-list.

Generally, no more than one net in a CD's group-list may be identifiedas selected at one time. A default net may be initially selected or theuser may select a net from the group-list.

The CM's SIP user-agent server of the MCU 252 response to an INVITErequest to join a net includes, as embedded content, the net's media andreal-time media signaling destination addresses, as well as other netparameters (such as media payload format descriptors). Once confirmed,the CD briefly displays feedback to the user, indicates whether the userhas listen-only privileges, and enables group service functions. If theCM 104 determines that the CD is not a member of the selected net, or anerror or other exceptional condition occur, the SIP server 252 respondswith a corresponding error response. When such a registration isrejected, the CD briefly displays a corresponding error message andgroup service functions remain idle. If no net is selected, groupservices within the CD remain idle.

As part of activating group services, the CD initializes and opens itsRTP media traffic channel 128 and the separate NBS media signalingchannel 124 to the CM destination addresses provided in a successfulinvitation response. Once these channels have been initialized,group-services are activated on the CD 108 and it enters thegroup-service quiet state 516 with the ability to receive voice trafficfrom the net and request permission to send voice traffic to the net.

With group services active, the CD 108 monitors its media traffic 128and signaling channels 124 to the CM. Voice data received on the mediatraffic channel 128 is decoded and presented using a CD 108 far-fieldspeaker or an ear-piece accessory, according to the current userconfiguration. The CD 108 displays the identity of the current speaker,as identified through real-time media signaling 124. If the identity ofthe current speaker is unavailable, the CD 108 displays the currentselected net name as listed in the group-list. The CD 108 may alsotabulate media traffic statistics (for example, total time spenttalking, listening, and monitoring, estimated media traffic receiptpacket loss) and make these available to the user as a diagnostic usinga menu option. While receiving traffic from the net, the CD 108transitions to the group-services listen state 520, returning to thequiet state 516 when voice traffic stops.

At any time, the user may request permission to speak to the net bydepressing the PTT button and causing the CD 108 to signal the CM 104(specifically, the MCU 252) with a floor-control request. The PIT buttonmay be any type of activation command, including, but not limited to,depressing a key or sequence of keys, voice activation, a switch, atoggling device, or dials. The MCU 252 responds by either granting ordenying the request. If the CD has listen-only privileges, such as CD112, (that is, the CD has a priority-level of zero within the selectednet), the request is denied. If denied, the CD 112 alerts the user withan error tone, displays a suitable error or explanatory message, andreturns to the quiet state 516. The CD insists that PTT be released anddepressed again before attempting another floor-control request. Ifgranted, the CD 112 enters the group-services talk state 524, signalsthe user with, for example, a brief audible chirp, and beginstransmitting voice traffic to the CM 104 for as long as PTT is keyed.The CM 104 may asynchronously signal the CD 112 (while PTT is keyed)that it has lost control of the floor. Upon receipt of such a signal,the CD 112 aborts transmitting voice traffic and alert the user with anerror tone until PTT is released, at which point it returns to the quietstate 516. Otherwise, once PTT is released, the CD 112 signals the CM104 that it has released the floor and returns to the quiet state 516.

A user may switch to a different net by selecting another net from thegroup-list whenever group-services within the CD 108 is in the quietstate 516, the listen state 520, or the dormant state 528. When a newnet is selected, the CD 108 signals the CM 104 to remove it from thecurrent net through SIP call-setup mechanisms and then follows similarprocedures to join the new net. If the process of joining the new netfails, the CD 108 is no longer a member of any nets and group serviceswithin the CD 108 returns to the idle state 504.

If the CM 104 determines that the CD 108 requesting the floor of aparticular net is the only registered member of the net in question, theCM 104 denies the floor-control request and signal an error message,such as a lonely-user error, which the CD 108 displays to the user.Although a net may exist with only one registered member, a net cannotrelay voice traffic unless there are least two registered members.

The NBS application is based on two distinct application-levelprotocols: the Session Initiation Protocol (SIP) call signaling asdescribed with respect to FIG. 11 and NBS Media Signaling as describedwith respect to FIGS. 12–14. SIP is used exclusively for call signalingand call setup. Media signaling carries PTT requests (FIG. 12) managesnet dormancy (FIG. 13), and resolves PTT arbitration conflicts (FIG.14).

SIP call signaling 350 is illustrated in FIG. 11. The Session InitiationProtocol provides NBS application-layer control (signaling) fordiscovering, joining and leaving NBS nets using the SIP server interface236 of the CM 104. To join a net, a CD 352 invites the net 100, by name,to participate in a call, through the top-level SIP server 236. To leavethe net 100, the CD 352 sends a corresponding “good-bye” to the net.

The CD 352 determines the IP address of the top-level SIP server 236 byusing the DNS 216 to resolve the provisioned primary or secondary SIPserver addresses into Internet network addresses, if necessary. As anoptional alternate approach, SIP conventions allow the CD 352 to querythe DNS 216 for service records associated with the NBS host systemdomain portion of the net address and contact the SIP server 236 at thereturned address(es).

By default, the CD 352 attempts to contact the SIP server 236 using adefault SIP port, unless alternate port information is determinedthrough DNS 216. Prior to attempting to join a net, the CD 352 may placea call using the SIP INVITE method to request an updated list ofavailable nets.

For example, the CD 352 that has brought up an over-the-air connectionis assigned an IP address and wishes to determine its current list ofavailable nets. This opens a UDP/IP connection to the SIP server portand issues a request. The request to obtain an updated list of nets isaddressed to a special destination. When appropriate, the CD 352 alsoincludes additional application-specific headers identifying the CDMAnetwork and system from which a CDMA cellular based CD 352 is obtainingservice.

The CD 352 may also include a header to indicate that the CD 352 expectsthat the SIP server 236 understands and supports NBS services. Theoption value distributed with the header can also be used by the CD 352to inform the server 236 of a specific version or type of NBS servicesthat the CD 352 expects the server 236 to support.

The CM's top-level SIP server 236 may redirect an invite request 356,using SIP redirection mechanisms, to a destination specifically definedto receive and respond to requests for net information. Upon receivingsuch a redirection, the CD 352 acknowledges (ACK) the response 357 andre-sends the request to the redirected destination.

The CD 352 may need to determine the appropriate SIP contact point forthe redirected address, through DNS mechanisms. To simplify this processfor the CD 352, the server 236 may specify the redirect destinationexplicitly using its Internet network address. Once an INVITE message354 requesting a list of nets is successfully received and accepted bythe server 236, the server 236 delivers an INVITE request response 356.

The INVITE request response 356 includes in its content a list ofrecords defining the set of nets that the CD 352 may subsequently join.The server 236 queries its net database 232 for nets that list therequesting CD 352 as a defined member to form the response 356 to theINVITE request 354. Nets are identified within the content using anapplication defined record format that includes the formal net-addressof the net. Nets may be listed in any order.

The server 236 may be unable to successfully respond to the CD 352 for avariety of reasons. In such circumstances, the server 236 delivers anappropriate SIP status code in place of the INVITE response 356. The CD352 should be prepared to accept and interpret such status codes, takingappropriate action (such as displaying an error message on the CD 352user interface display) in the case of any fatal errors. The server 236may also preface a successful INVITE response 356 with informationalstatus responses indicating the progress of the registrations. The CD352 may accept and interpret informational status codes that prefacesuccessful registrations.

The CD 352 requests to join a net by issuing a SIP INVITE request 358 tothe CM manager 240 through the server 252. If the CD 352 does not havean open UDP/IP connection to the SIP server 252, it will open a newUDP/IP connection to the SIP server port.

The CD 352 is prepared to be redirected by the top-level SIP server 236and re-issue the request to the redirected destination if necessary. TheCM's top-level SIP server 236 redirects any incoming INVITE request asappropriate to the MCU's SIP server 252 currently associated with thenet in question. The CD 352 may be redirected more than once.

The INVITE request 358 may include a description (as message content) ofthe media sources that originates with the CD 352, assuming theinvitation succeeds. If included, the description is included as messagecontent and described using field constructions.

The session description is delivered in a format compatible with theSession Description Protocol (SDP). After defining the SDP version (v),the session description includes a mandatory origin (o) description. TheCD 352 may use any convenient mechanism for choosing the values for thesession identifier and session version. Providing an estimate of thecurrent time is one possible way of defining the session identifier.Connection data (c) is specified by defining the network type, addresstype, and connection address. The CD 352 uses the IP address with whichit labels (or source) media traffic as the connection address. The CD352 uses the name portion of the net's net-address as the session name(s). The CD 352 specifies the lifetime (t) of the session by providingits best estimate of the start or current time, preferable in NetworkTime Protocol (NTP) format, and indicates that the session is unbounded(O). The media format (m) description defines the media type, sourceport, transport protocol, and payload format that the CD 352 intends touse to transmit to the net. Finally, the session description uses anattribute (a) type definition to indicate that the CD 352 expects thesession to be operated as a NBS conference. The server 236 shouldconfirm that the invited to address is indeed a valid NBS net addressbefore granting the invitation.

To indicate a successful invitation, and specifically inform the CD 352that it has been added to the list of participants for the invited net,the server 236 delivers an INVITE response 360.

A successful INVITE response 360 includes the primary sessiondescription for the invited net, which describes supported media trafficports and formats using SDP syntax. The session description includes aconnection (o) description that defines the network address to which allmedia signaling and traffic should be sent. The net's media destinationnetwork address is not necessarily the same as the SIP user-agentserver's network address resolved using DNS from the net's net-address.

The session description describes all media and destination media ports.The session description should also include an identifier assigned tothe CD 352 by the MCU 252 for the purpose of identifying media signalingmessages transmitted by the CD 352 as part of its subsequentparticipation in the net. The value of this identifier is unique amongall active participants on a given net and should thus be generateddynamically. The CD 352 does not necessarily cache this identifierbetween successful SIP invitations.

The session description may also include an NBS protocol versionannouncement indicating the revision level to which the net's mediasignaling adheres. Such an announcement may be implemented by extendingthe value of the type attribute field or defining a new attribute, whosevalue is the protocol version number.

After receiving a successful INVITE response, the CD 352 confirms theinvitation by sending a SIP acknowledge (ACK) request 362 back to thenet's MCU's SIP user-agent server 252. After transmitting the ACKrequest 362, the CD 352 may close its TCP connection with the SIPserver. Prior to the ACK request 362 being transmitted, the CD 352initializes its media signaling and traffic ports according to thesession description delivered in the INVITE response 360.

At any time after the CD 352 has transmitted the SIP ACK message 362 inresponse to a successful INVITE response 360, the CD 352 may formallyterminate its participation in the net by sending a SIP BYE message 364to the net's user-agent server 252. Prior to sending the BYE message364, the CD 352 may need to open a TCP connection to the user-agentserver 252. The BYE message 364 is acknowledged by the CM with a BYEresponse message 366. Once the BYE response message 366 is acknowledged,the CD 352 may close its UDP connection with the user-agent server 252.Prior to acknowledging the BYE response message 366, the user-agentserver 252 removes the CD 352 from the indicated net's list of activeparticipants.

In general, a SIP user-agent client of the CD 352 may use the OPTIONSmethod to query a SIP server's capabilities. In particular, the CD 352might wish to query an arbitrary SIP destination to determine whetherthe destination provides NBS call-signaling support.

The CD 352 may wish to abort a pending INVITE request 358 prior toreceiving the INVITE response 360 and sending the acknowledgement 362.In such circumstances, the CD 352 may use a SIP CANCEL (not shown)method to gracefully abort the call. Both the top-level SIP redirectserver 236 and the CM's SIP user-agent server 252 support the CANCELmethod.

For example, the CD 352 may use the CANCEL method to abort an INVITEmessage 358 in progress if the user decides to place a voice-servicescall and presses send before the INVITE message 358 completes. In such acircumstance, rather than wait for the INVITE response 360 to completeand immediately send the BYE message 364, the CD 352 may simplyimmediately CANCEL the INVITE message 358 and proceed to place therequested voice-services call.

After the CD 108 has successfully negotiated entry into the currentmembership of a NBS net using SIP, all real-time call control takesplace through point-to-point application level media signaling messagesexchanged between each CD 352 and the net's MCU SIP server 252.

Media signaling messages are transported using the protocol stackdepicted in FIG. 4, and in accordance to the sequence depicted in FIG.12. FIG. 12 illustrates a media signaling message sequence 368. A PTTrequest message 370 is sent by the CD 352 to the SIP user agent server252 of the MCU node 208 and signals a user's desire to broadcast media,usually voice, to the net. Normally, the PTT request message 370 is sentfor each press of the CD 352 push-to-talk button to denote afloor-control request. In addition, a PTT release message is sent by theCD 352 to the SIP user agent server 252 to denote the normal release ofthe “floor” when the user releases the CD 352 push-to-talk button.

The PTT message comprises of fields such as the opcode, id, src, andreserved. The opcode field defines whether the PTT message is afloor-control request or release message. The id field provides a uniquemessage identifier to allow subsequent PTT release and PTX messages toreference a specific PTT request. The id should be unique within theregistration session of a particular CD 352. The src field uniquelyidentifies the CD 352 that sends the PTT request 370 to the SIP useragent server 252. The reserved field reserves space in the PTT message370 for future capabilities.

The CD 352 expects to receive at least one PTX response message 372 forevery transmitted PTT request 370. If a PTX response 372 is not receivedwithin a predetermined timeout period, the CD 352 assumes the PTTrequest 370 was lost in transit and retransmits the PTT message 370using the same PTT id.

If a PTX response message 372 is never received from the SIP user agentserver 252 within a predetermined number of retransmits, the CD 352assumes that SIP user agent server 252 is no longer reachable,transitions to NBS idle mode, and indicates an error condition to theuser. In a preferred embodiment, the CD 352 uses a different PTT id forthe request and release messages.

The PTX message 372 is sent by the SIP user agent server 252 to a CD 352to acknowledge and respond to a previous PTT request 370, as well as tosignal asynchronous floor-control events. The SIP user agent server 252uses the PTX message 372 to respond to a PTT floor-control request orrelease. The PTX message 372 includes information such as to whether thereferenced floor-control request was granted or denied. When respondingto a PTT floor-control release 370, the PTX message 372 is used toindicate confirmation of receipt only. The SIP user agent server 252 mayalso use the PTX message 372 to asynchronously deny a previously grantedfloor-control request (when a higher priority CD 352 issues afloor-control request, the PTX grant expires (i.e., times out), or someother event occurs requiring that control of the net's floor berevoked).

The PTX message 372 comprises fields such as opcode, id, action, status,and expires. The opcode field defines whether the PTX message 372 is asynchronous response to an outstanding PTT request, or if it is anasynchronous message indicating an error or priority arbitrationconflict. The id field references a previously received PTT request. Theaction field indicates whether the PTX message 372 is granting, denying,revoking, or confirming control of the net's floor. The status fieldprovides additional information explaining the PTX action, particular incases when the PTX message 372 denies, revokes, or cannot act upon theprior PTT request. The status field may indicate that a higher prioritytalker has been granted control of the net, or that the CD 352 is notlisted as a net participant and hence is not allowed to submit mediasignaling requests for the net. The expires field represents the maximumduration, in whole seconds, for which the control of the net's floor isgranted to the receiving CD 352. The SIP user agent server 252 startsits timer from the instant it sends the PTX message 372 response, notwhen the CD 352 begins sending media traffic. The value of the expiresfield is a configurable net parameter.

The CD 352 does not explicitly acknowledge receipt of the PTX messageresponse 372. Instead, if the transmitted PTX message response 372 islost, the CD 352 PTT retransmit timer expires and the CD 352 retransmitits PTT request 370. Since the retransmitted PTT 370 has the same id asthe lost PTX response 372, the SIP user agent server 252 responds byre-sending the lost PTX message response 370, rather than treating theretransmitted PTT message request 372 as a separate push-to-talk requestevent.

A PTA message 374 is sent by the SIP user agent server 252 to each CD352 currently participating in a net to announce the identity of thesource of pending media traffic. A PTA message 374 is also used toformally announce the end of a talk-spurt.

The PTA message 374 comprises fields such as opcode, talker, andreserved. The opcode field indicates whether the PTA message 374 isannouncing the granting (or release) of the floor to (or by) the CD 352identified by talker. The talker field identifies the CD 352, whichsources media traffic to the net until the next PTA message 374 is sent.The reserved field reserves space in the PTA message 374 for futurecapabilities.

The CD 352 whose PTT floor-control request 370 was successful may or maynot receive a PTA message 374 announcing it has control of the floor.The message may arrive before or after it receives the corresponding PTXresponse 372, since UDP does not necessarily preserve datagram ordering.However, the SIP user agent server 252 sends the PTA announcement 374before it expects to begin forwarding media (in the case of a PTA grantannouncement). It is recommended that the requesting CD 352 ignorereceived PTA messages 374 that announce it has won control of the floorand rely only on the receipt of a PTX grant message response 374 todetermine whether it can begin transmitting media to the net.

An “are you there” AYT message 404 (FIG. 13) is sent by the SIP useragent server 252 to an individual CD 352 in order to confirm that the CD352 in question is reachable using IP. A collection of AYT messages 404may also be sent to a group of net participants in order to signal thata net is no longer in dormant mode.

The AYT message 404 comprises fields such as opcode, id, and reserved.The opcode field indicates whether the MCU node 208 is sending the AYTmessage 404 to determine whether the CD 352 is still reachable or if theSIP user agent server 252 is using the AYT message 404 traffic to bringthe net's associated CDMA cellular traffic channels out of dormant mode.The id field provides a unique message identifier to allow a subsequent“I am here” IAH response message 408 to reference a specific AYT requestmessage 404. The id may include a timestamp reference for generatinglatency estimates. The reserved field reserves space in the AYT message404 for future capabilities.

The CD 352 may or may not be in dormant mode when an AYT message 404 issent. In all cases, the CD 352 responds to a received AYT message 404with an IAH response message 408.

The SIP user agent server 252 assumes that the CD 352 generally respondsto an AYT message 404 with an IAH response 408. If an IAH response 408is not received within a reasonable timeout, the SIP user agent server252 transmits a new AYT message 404 with a new id. If after aconfigurable number of retransmits, a response to the AYT message 404 isnot received from the CD 352, the CD 352 is assumed to be unreachableand the SIP user agent server 252 removes it from the current list ofnet participants. Future media signaling messages from the removed CD352 will be ignored (or will generate an error response) until the CD352 successfully re-joins the net.

The IAH message 408 is sent by the CD 352 to the SIP user agent server252 to acknowledge receipt of a previously sent AYT message 404. The IAHmessage 408 comprises fields such as id, src, and reserved. The id fieldreferences a previously received AYT message 404 that the CD 352 isacknowledging. The src field uniquely identifies the CD 352 that sendsthe IAH message 408 response to the SIP user agent server 252. Thereserved field reserves space in the IAH message 408 for optionalcapabilities.

The SIP user agent server 252 assumes that the CD 352 acknowledges allreceived AYT messages 404 with an IAH response message 408. If thereferenced AYT message 404 was sent to confirm that a CD 352 remainsconnected in the NBS quiet state, passively monitoring NBS media trafficand signaling, the SIP user agent server 252 notes the time of the IAHreceipt 408 for future reference.

Since the SIP user agent server 252 is responsible for defining thevalue of the id field, the SIP user agent server 252 may use the id todetermine and track whether a specific CD 352 remains reachable.

The ZZZ or sleep message (illustrated in FIG. 13 as reference numeral412) is sent by the SIP user agent server 252 to the CD 352 to encouragethe CD 352 to release its over-the-air resources and enter dormant mode.The CD 352 may choose to ignore this message (especially if it isconcurrently supporting other packet applications).

The ZZZ message comprises fields such as id and reserved. The id fieldprovides a unique message identifier to allow the CD 352 todifferentiate between multiple receipts of the ZZZ message. The reservedfield reserves space in the ZZZ message for optional or futurecapabilities.

The CD 352 does not acknowledge receipt of the ZZZ message. Errorrecovery is generally not attempted if the ZZZ message is lost. To guardagainst a ZZZ message being lost, the SIP user agent server 252 may sendmultiple copies of the same ZZZ message to an individual CD 352. The SIPuser agent server 252 insures that copies of the same sleep message aresent within a defined interval, and the CD 352 waits for a period longerthan this interval from the time the first sleep message (with a new id)is received before releasing its over-the-air link and transitioning toa dormant state.

As illustrated in FIG. 15, an ASK message 382 is sent by the CD 352 as aquery 384 to the SIP user agent server 252 to confirm connectivity withthe SIP user agent server 252. The ASK message 382 also allows the CD352 to determine whether the CD 352 remains listed as a net participant.The CD 352 may confirm its participation after a service-disruption orother period where it may have temporarily lost connectivity with theSIP user agent server 252.

The ASK message 382 comprises fields such as id, src and reserved. Theid field provides a unique non-zero message identifier to allow asubsequent FYI response message to reference a specific ASK requestmessage. The src field uniquely identifies the CD 352 that sends the ASKmessage 382 request to the SIP user agent server 252. The reserved fieldreserves space in the ASK message 382 for optional or futurecapabilities.

The CD 352 assumes that the SIP user agent server 252 responds to areceived ASK message 382 with an FYI response message 386. If an FYIresponse 386 is not received within a predetermined timeout period, theCD 352 transmits a new ASK message 382 with a new id. If after aconfigurable number of retransmits, a response to the ASK message 382 isnot received from the SIP user agent server 252, the SIP user agentserver 252 is assumed to be unreachable and the CD 352 transitions tothe group-service idle state.

The FYI message 386 is sent by the SIP user agent server 252 to the CD352 to acknowledge receipt of a previously sent ASK message 382 or issent asynchronously by the SIP user agent server 252 to inform the CD352 of an exceptional condition.

The FYI message 386 comprises fields such as opcode, action, status, id,and reserved. The opcode field defines whether the FYI message 386 is asynchronous response to an outstanding ASK request 382, or if it is anasynchronous message indicating an exceptional condition. The actionfield indicates whether the FYI message 386 is confirming netparticipation, informing the CD 352 that it has been administrativelydeleted from the net's member list, or performing some other to bedefined function. The status field provides additional informationexplaining the FYI response 386, particular in cases when the FYImessage 386 indicates that the CD 352 is not a net participant ormember. The id field references a previously received ASK message 382that the CD 352 is acknowledging. In value of the id field is undefinedfor asynchronous FYI responses. The reserved field reserves space in theIAH message 408 for optional or future capabilities.

The CD 352 generally does not acknowledge receipt of FYI message 386responses. If a synchronous FYI message 386 response is lost, the CD 352sends a new ASK message 382 request. Because the CD 352 does not requestasynchronous FYI message 386 responses, in a preferred embodiment theSIP user agent server 252 make at least three staggered transmissions ofany asynchronous FYI message 386 responses.

A participating CD 352 signals a user's desire to broadcast media to thenet by issuing a PTT message request 376 to the SIP user agent server252. The SIP user agent server 252 responds to the PTT request 376 witha PTX message response 378 that may either grant or deny the request. Ifthe request is granted, a PTA announcement message 380 is broadcast toall net participants. The user-interface of the requesting CD 352 mayindicate to the user that permission to talk to the net has been grantedas soon as the granting PTX message response 378 is received. The CD 352normally broadcasts media traffic until the user releases the PTT buttonat which point it signals the end of the talk-spurt by issuing a PTTrelease message 376 to the SIP user agent server 252. The SIP user agentserver 252 responds with a PTX confirmation message 378 and broadcastsan announcement signifying the end of the talk-spurt to all netparticipants.

When any CD 352 has the floor (the right to talk) of a net, the net issaid to be active; otherwise, it is inactive. If a net is inactive for atime exceeding the net's hang-time, the SIP user agent server 252 mayput the net in dormant mode by individually signaling all registeredmobile stations to release their over-the-air traffic channels. Aconnection is maintained to allow a floor-control request or othertraffic to bring the net out of dormant mode relatively quickly. Netmembers may ignore “go dormant” messages. The SIP user agent server 252does not explicitly or implicitly track the dormancy status ofindividual net members.

As illustrated in FIG. 15, the SIP user agent server 252 will “wake-up”a net and bring it out of dormant mode 618 when a successfulfloor-control request 704 is received during dormancy. As soon as thefloor-control request 704 has been granted, the SIP user agent server252 will signal each registered CD 352 by requesting the are-you-there(AYT) message 716 over the media-signaling channel and start an internalwake-up timer 724. Each CD 352 acknowledges receipt of the AYT message716 to the SIP user agent server 252 if it wishes to remain registeredin the net. Optionally, a dormant CD 352 may buffer media traffic 740from the time the user keys PTT until the CD 352 traffic channel is(re)connected. The SIP user agent server 252 may buffer media traffic740 received from the talking CD 352 until the wake-up timer 724 exceedsthe wake-up timeout, at which point, it begins forwarding media trafficto each registered CD 352, including any members that have not yetresponded to the AYT request 716. Thus, both the CD 352 and the MCU node208 have the ability to buffer data until the recipient is ready toreceive the buffered information. In an embodiment, portions of data arestored both in the CD 352 and the MCU node 208.

The SIP user agent server 252 periodically retransmits AYT requests 716to any registered CD 352 that has not acknowledged receipt of the AYTrequest 716. Once the wake-up timer 724 has exceeded a second longerlate-riser timeout, the SIP user agent server 252 will unregister anymember CD 352 whose AYT acknowledgement is outstanding and stop thewakeup timer 724. The SIP user agent server 252 ignores duplicate AYTrequests.

If the CD 352 attempts to join a net that is currently dormant, the SIPuser agent server 252 processes the request normally and then signal theCD 352 to go dormant. The signaled CD 352 may ignore the go-dormantcommand.

During periods of extended net inactivity, the NBS allows for a packetdata service call to be placed in the dormant/idle state 528 (see FIG.10). The SIP user agent server 252 facilitates transitions into and outof the dormant/idle state 528 by independently managing a similardormancy concept for each NBS net 100.

FIG. 13 illustrates the sequence of media signaling messages withrespect to dormancy 400 between the CD 352 and the SIP user agent server252. In general, a message is sent to all CDs in the net to go dormantbased on a control signal sent from the CM, based on a timer in each CD.As such, resources allocated to the net are released and may be used forother users. On a configurable schedule, the SIP user agent server 252sends a message request (AYT) 404 to each CD 352 for the purpose ofconfirming that the CD 352 in a quiet state remains reachable. Thus, theCM 104 maintains centralized polling of current users of the net andtheir status. This also allows individual CDs to dynamically join orleave the net. The CD 352 responds to the AYT request 404 with a messageresponse (IAH) 408. The AYT messages 404 are not necessarily broadcastto each CD 352 at the same time. The SIP user agent server 252 maystagger sending AYT messages 404 to each net participant to avoidreceiving a flood of simultaneous IAH message responses 408.

After the net has been idle long enough for the net's configurablehang-time to expire, the SIP user agent server 252 broadcasts a ZZZrequest message 412 to every net participant. In response, each CD 352may release its over-the-air resources and enter dormant mode. Netparticipants need not necessarily respond to the ZZZ request message412.

A successful PTT request 416 by the CD 352 brings the net out of dormantmode. In an embodiment, a predetermined threshold number of users areneeded to respond in order to bring the net out of dormancy. Prior togranting the request with a PTX message 420, the SIP user agent server252 sends every CD 352 an AYT message request 424 to force eachpreviously participating CD 352 out of dormancy. This is done if the CD352 chose to release its over-the-air resources in response to the ZZZmessage 412, and to confirm that the participating CD 352 still remainsreachable. In another embodiment, After a configurable but fixed delay,defined as the PTX dormancy response timer, the SIP user agent server252 transmits the PTX grant message response 420 to the requesting CD352. Once a second wake-up timer (whose value is generally not less thanthe PTX dormancy response timer) expires, the SIP user agent server 252announces the talker via a PTA message 428 to all net participants andmay begin forwarding media.

The MCU node 208 is responsible for receiving incoming data packets fromthe transmitting CD 352 and for sending duplicate copies of the receiveddata packets to other members of the net to which the transmitting CD352 belongs. As each data packet is received by MCU node 208, it isstored in a memory (not shown). The transmitting CD 352 may beidentified by interrogating the data packet. In one embodiment, an IPaddress representing the transmitting CD is included in each data packetas a way to perform the identification.

After the transmitting CD 352 is identified, the MCU node manager 256retrieves a list of net members belonging to the net associated with theparticular MCU node 208 from local memory (each MCU is typicallyassigned to one net only). A destination address is associated with eachactive net member, i.e., net members who are presently registered withMCU node 208, in local memory. In one embodiment, the destinationaddress is an IP address. MCU node manager 256 then creates a duplicateof the original data packet, except that the destination addressidentified within the data packet is modified to reflect the destinationaddress of the first net member. Next, MCU 208 creates a secondduplicate data packet, addressed to the second net member. This processcontinues until the original data packet has been duplicated and sent toall of the active net members identified in local memory. During theplay-out of any buffered media, the CM 104 treats the net as active,even if the talking CD 352 has released the floor. Hence, the CM 104does not allow a CD 352 to interrupt the play-out of buffered mediaunless the interrupting CD 352 has higher priority than the source ofthe buffered media.

Note that the SIP user agent server 252 may receive IAH messageresponses 432 for an extended interval after the net is brought out ofdormant mode and that the SIP user agent server 252 does not wait forall net participants to respond before granting the pending PTT request416. Late responders whose LAH response 432 arrives after the PTX grantmessage response 420 is transmitted remains listed as net participants,but may not receive all initial media traffic and signaling. Any CD 352that does not respond to the AYT request 424 after a third larger (andconfigurable) delay are generally assumed to no longer be reachable andare removed from the net's list of active participants.

FIG. 14 illustrates a sequence of NBS media signaling messages 440demonstrating a higher priority CD 444 interrupting a lower priority CD442 with control of the net's floor.

Initially, a lower priority CD 442 submits a PTT message request 446 tothe SIP user agent server 252 that is granted by the SIP user agentserver 252. The SIP user agent server 252 announces that the CD 442 hascontrol of the net's floor.

While the lower priority CD 442 is transmitting media 443, a second CD444 attempts to interrupt by sending the SIP user agent server 252 a PTTmessage request 448 for the same net. The SIP user agent server 252determines that the second CD 444 has higher priority than the talkingCD 442 and immediately revokes control of the net's floor from thetalking CD 442 by sending it an asynchronous PTX denial message 454. TheSIP user agent server 252 then grants the PTT request 448 to the higherpriority CD 444 with a normal PTX grant message response 452 andannounces that the higher priority CD 444 has control of the net'sfloor.

If the SIP user agent server 252 determines that the interrupting CD 444does not have higher priority, the SIP user agent server 252 immediatelyrejects the PTT request 448 with a PTX message response 452 andcontinues to distribute media 456 from the talking CD to the net'sparticipants without interruption.

Although the priority assigned to a particular CD is a fixed valuedefined in the database maintained by the SIP user agent server 252, theSIP user agent server 252 may use other arbitration algorithms that donot necessarily always grant the floor to the highest-priorityrequesting participant, as depicted here. The PTT arbitration algorithmused to arbitrate conflicts can be individually configured on a per netbasis.

At a minimum, the SIP user agent server 252 supports an arbitrationpolicy that allows a CD to interrupt the current talker only if the CDhas a priority level that exceeds that of the current talker. An CD withminimal priority can listen to media traffic but never gain control ofthe net's floor.

FIGS. 15 and 16 illustrate operation of the CM 104 and CD 352,respectively, during various states. The CM 104 maintains an inactivitytimer for each net, or the hang-time timer 620. When the inactivitytimer 620 reaches a configurable prescribed value, the timer triggersthe CM 104 to place the net in a dormant state 618 by broadcasting amedia signaling message 696 to all net participants. Upon receipt of themessage, a participating CD 352 may release its traffic channel andenter a dormant/idle state 844, or the CD 352 may ignore the message andremain in a connected state 820. In particular, net participants thatare not operating over a channel, such as dial-up PSTN users, shouldignore the media signaling messages.

The net's hang-time timer 620 does not advance for the duration that aPTX grant message response 632 is an effect. The timer 620 is reset tozero when the PTX grant message 632 is transmitted and remain at zerountil the PTX grant 632 expires or the CD 352 releases the net's floor872. Once the floor is released, the hang-time timer advances until thenext PTX grant message response 632 is transmitted.

If a participating CD 352 enters the dormant/idle state 844, it remainsdormant until either packet data addressed to the CD 352 arrives at theCD 352 MA cellular infrastructure or the CD 352 generates data to sendusing the packet data service. The former case may be triggered bytraffic sent to the CD 352 by the CM 104 (908). The latter case may betriggered by the user keying the PTT button to request permission tobroadcast 824 to the net. Other triggers unrelated to NBS are alsopossible.

The net itself remains dormant until one or more participants triggerthe transmission of a PTT request 704. If the CM 104 determines it cangrant the PTT request message 704 (including performing any necessaryarbitration to deal with multiple requests) it sends a request 716 toeach listed net participant to trigger a transition out of thedormant/idle state 844. For any specific CD 352, the trigger may or maynot be necessary, but each CD 352 nonetheless responds to the request.In this circumstance, when a net is transitioning out of the dormantstate 618, the CM 104 refrains from sending the initial PTX grantresponse message 756 until a fixed but configurable delay, the PTXdormancy response timer 728, expires. After the timer 728, whose defaultvalue is typically be zero, expires, the CM 104 sends the PTX grant 756as usual. However, the CM 104 continues to refrain from forwarding mediato the net until a second related timer, the net's wake-up timer 724,expires. Both timers reset when the CM 104 determines that the dormantnet's floor can be granted. The value of the wake-up timer 724 shouldnot be less than the value of the PTX dormancy response timer 728. Afterthe wake-up timer 724 has expired, the CM 104 begins forwarding mediaand media signaling and traffic flow normally. Both timers areconfigurable on a per net basis.

If the CM 104 determines that it cannot grant the PTT request 704, itimmediately signals the requesting CD 352 accordingly with a PTX denymessage 708, and the net remains dormant.

A CD 352 that has entered the Dormant/Idle state 844 may require asystem change, change service options, or experience some other servicedisruption that causes it to never receive and respond to the AYT“wake-up” message 908. The CM 104 maintains a third longer timer thatalso resets with the wake-up and PTX dormancy response timers. Thislonger late-riser timer (not shown) is also configurable on a per netbasis. After the late-riser time expires, any CD 352 whose IAH response916 to the AYT wake-up message 908 has not been received is removed fromthe net's list of active participants by the CM 104. Any such removed CD352 to re-registers with the CM 104's SIP server 236 in order to onceagain become a net participant.

Due to potential delays associated in transitioning a CD 352 out of theDormant/Idle state 844 to the connected state, both the CD 352 and theCM 104 may perform voice buffering to mitigate the transition delayperceived by the user.

Typically, the CD 352 user-interface signals the user, through visual oraural mechanisms, at least two milestones in the processing of a PTTkey-press. First, the CD 352 signals that it has detected a PTTkey-press. Later, the CD 352 signals that it has received the CM 104'sPTX message response 868. If the PTX message response 868 grantspermission to broadcast media, the CD 352 user-interface provides anindication that the user may begin talking to the net; otherwise, the CD352 user-interface indicates that the user has been denied permission856 to talk to the net.

When the net is not dormant, the latency between the transmission of thePTT request message and receipt of the corresponding PTX responsemessage is relatively small, and the user grows accustomed to beinggranted permission to speak shortly after PTT button is keyed. However,when the net is dormant, a relatively significant delay may separatetransmission of the PTT request 852 and receipt of the corresponding PTXmessage 856 or 868. The delay may occur because the CD 352 may havereleased its traffic channel and experiences a delay in re-establishingpacket data service. The delay may also occur because the CM 104 waitsuntil the net's wake-up timer has expired before sending the PTX messageresponse 856 or 868. In this circumstance, the CD 352 may optimisticallyassume that the CM 104 eventually responds with a PTX grant response 868and signal the user that the PTT request 876 has been granted. To allowthe user to begin speaking “early,” the CD 352 buffers voice internally,until either the PTX request arrives, or it consumes all availableinternal buffer space.

If the PTX message response arrives and the request is granted, the CD352 may begin transmitting the (buffered) voice and operation proceedsnormally. If the PTX message response arrives and the request is denied,the CD 352 signals the user that permission to talk to the net has beendenied. Since the user has already started talking, this late denial mayappear to be a priority conflict. Special care is taken in thiscircumstance to avoid unnecessarily confusing the user. The CM 104signals the PTX deny message 856 as soon as possible to limit the lengthof time the user may talk under the assumption that the outstanding PTTrequest eventually will be granted.

If the PTX message does not arrive before all available internal bufferspace is consumed, the CD 352 may simulate a PTX deny message 856 andsignal the user to stop talking 856. If the CD 352 has not been able tore-establish service, it may also need to take other error action atthis point and inform the user accordingly. Alternatively, if by thistime, packet data service is re-established, the CD 352 may, in thissituation, begin transmitting voice media to the CM 104 without priorreceipt of a PTX grant message response 868.

While waiting for the wake-up timer to expire, the CM 104 buffers anyvoice media received on a net's media channels from the CD 352 that hassent the outstanding PTT request 852 and eventually sends acorresponding PTX grant response 868. Once the wake-up timer expires,the CM 104 transmits the PTX grant response 868 to the requesting CD352, broadcasts a PTA announcement to the net, and begins broadcastingthe buffered voice media. If the CM 104's internal voice buffer isconsumed before the wake-up timer expires, the CM 104 immediatelytransmits a PTX denial message 856 to the requesting CD 352. Thetreatment of the buffered voice is undefined, but the CM 104 maytransmit the contents of its voice buffer to the net after the wake-uptimer has expired. Once the wake-up timer has expired, net operationproceeds normally.

The size of the voice media buffer in the CD 352 is chosen based on themaximum time expected to transition to the IS-707.5 connected state 812from the IS-707.5 dormant/idle state 844. Similarly, the size of themedia buffer in the CM 104 should be chosen based on the (maximum) valueof the net's wake-up timer specified in the CM 104's net database 232.

A more complete description of the states of the CM 104 follows. The CM104 implements the NBS Media Signaling state diagram 600 shown in FIG.15 for each instance of a net. The CM 104 initializes in an idle state604 when a net is created. The net remains in the idle state 604 as longas no net participant request PTT 608 is granted for control of thefloor 612 and the net is not dormant 618. The CM 104 resets thehang-time timer 620 to zero upon entering the idle state 604. The CM 104transitions from the idle state 604 to the grant state 612 when a PTTrequest 608 from a net participant is received. The CM 104 transitionsfrom the idle state 604 to the go-dormant state 624 when the hang-timetimer expires.

The CM 104 transitions from the grant state 612 to the idle state 604and sends a PTX deny 626 response to the requesting CD 352 if thearbitration algorithm denies control of the floor to the requesting CD352. The CM 104 transitions from the grant state 612 to the announcestate 628 and sends a PTX grant response 632 to the requesting CD 352 ifthe arbitration grants control of the floor to the requesting (orinterrupting) CD 352. After sending the PTX grant response 632, the CM104 considers the requesting (or interrupting) CD 352 the net's currenttalker. The CM 104 transitions from the announce state 628 to the talkstate 636 and sends a PTA message 640 announcing the new talker to allnet participants immediately upon entering the announce state 628. Thecurrent talker remains in the talk state 636 as long as no PTT request644 or release message 648 is received from a net participant and thenet's failsafe timer 652 has not expired. The CM 104 resets the net'sfailsafe timer 652 upon entering the talk state 636. While in the talkstate 636, the CM 104 broadcasts media from the net's current talker tothe net.

The CM 104 transitions from the talk state 636 to the arbitrate state656 when the PTT request message 644 is received from a net participant.The CM 104 transitions from the talk state 636 to the release-confirmstate 660 when the PTT release message 648 is received from the CD 352with control of the net's floor. The CM 104 transitions from the talkstate 636 to the failsafe-recover state 664 when the failsafe timer 652expires. The user is typically given the amount of time remaining beforethe failsafe timer expires. The CM 104 broadcasts media traffic receivedfrom the net's current talker to the net while it remains in the talkstate 636. If the net's media buffer is not empty, the CM 104 continuesto buffer media received from the net's current talker while itbroadcasts media traffic to the net.

The CM 104 enters the arbitrate state 656 as a result of receiving thePTT request message 644 while in the talk state 636. The CD 352 thatoriginated the PTT request message 644 is known as the interruptingparticipant. If the interrupting participant and the current talker areidentical, the CM 104's PTX grant message 668 was lost and the currenttalker is re-sending its PTT request 644. The CM 104 transitions fromthe arbitrate state 656 to the talk state 636 and sends the interruptingparticipant the PTX grant message 668 if the interrupting participantand the net's current talker are identical. The CM 104 applies thearbitration algorithm to the net's current talker and the interruptingparticipant immediately upon entering the arbitrate state 656 if theinterrupting participant and the net's current talker are distinct.

The CM 104 transitions from the arbitrate state 656 to the talk state636 and sends the interrupting participant a PTX deny message 672 if thearbitration algorithm rules in favor of the current talker. The CM 104transitions from the arbitrate state 656 to the grant state 612 andsends the net's current talker a PTX interrupt message 676 if thearbitration algorithm rules in favor of the interrupting participant.The CM 104 transitions from the release-confirm state 660 to therelease-announce state 680 and sends a PTX confirm message 684 to thecurrent talker immediately upon entering the release-announce state 680.

The CM 104 transitions from the failsafe-recover state 664 to therelease-announce state 680 and sends a PTX deny message 688 to thecurrent talker immediately upon entering the failsafe-recover state 664.The CM 104 transitions from the release-announce state 680 to the idlestate 604 and sends a PTA release announcement 692 to all netparticipants immediately upon entering the release-announce state 680.The CM 104 transitions from the go-dormant state 624 to the dormantstate 618 and sends a ZZZ message 696 announcing the net has gonedormant to all net participants immediately upon entering the go-dormantstate 624. The net's state machine remains in the dormant state 618 aslong as no net participant requests control of the floor. The CM 104transitions from the dormant state 618 to the wakeup state 706 when aPTT request 704 from a net participant is received.

The CM 104 transitions from the wakeup state 708 to the dormant state618 and sends a PTX deny response 708 to the requesting CD 352 if thearbitration algorithm denies control of the floor to the requesting CD352. Since the net is dormant, this can happen only if the requesting CD352 has listen-only privileges. The CM 104 transitions from the wakeupstate 706 to a wakeup-pending state 712 and sends a AYT wakeup request716 to all net participants if the arbitration grants control of thefloor to the requesting CD 352. After sending the AYT wakeup request716, the CM 104 considers the requesting CD 352 the net's pendingtalker.

The CM 104 remains in the wakeup-pending state 712 as long as no PTTrequest message 720 is received from a net participant, a wake-up timer724 has not expired and the a PTX dormancy response timer 728 has notexpired. The CM 104 resets the wake-up timer 724 and the PTX dormancyresponse timer 728 upon entering the wakeup-pending state 712. The CM104 transitions from the wake-up pending state 712 to thedormant-arbitrate state 732 when the PTT request message 720 is receivedfrom a CD 352 distinct from the net's pending talker. The CM 104transitions from the wake-up pending state 712 to a dormant-grant state736 when the net's wake-up timer 724 expires. The CM 104 transitionsfrom the wake-up pending state 712 to a buffered-grant state 740 whenthe PTX dormancy response timer 728 expires.

The CM 104 applies the arbitration algorithm to the net's pending talkerand the interrupting participant immediately upon entering thedormant-arbitrate state 732. The CM 104 transitions from thedormant-arbitrate state 732 to the wake-up pending state 712 and sendsthe interrupting participant a PTX deny message 744 if the arbitrationalgorithm rules in favor of the pending talker. The CM 104 transitionsfrom the dormant-arbitrate state 732 to the wake-up pending state 712,sends the pending talker the PTX deny message 744, and considers theinterrupting participant to be the net's new pending talker if thearbitration algorithm rules in favor of the interrupting participant.

The CM 104 transitions from the dormant-grant state 736 to the announcestate 628 and sends a PTX grant response 748 to the net's pending talkerimmediately upon entering the dormant-grant state 736. The CM 104transitions from the buffered-grant state 740 to a buffering state 752and sends a PTX grant response 756 to the net's pending talkerimmediately upon entering the buffered-grant state 740. The net's statemachine remains in the buffering state 752 as long as the wake-up timer724 has not expired. While in the buffering state 752, the CM 104buffers any media traffic received from the net's pending talker.

The CM 104 transitions from the buffering state 752 to the announcestate 628 when the wake-up timer 724 expires. The CM 104 buffers anymedia traffic received from the net's pending talker in the net's mediabuffer while it remains in the buffering state 752. The CM 104 respondsto any media signaling request that contains invalid or reserved fieldvalues by sending an ERR response 760 in an error state 764 to the CD352 that sent the message and otherwise ignore the request.

The CD 352 implements the NBS Media Signaling state diagram 800 shown inFIG. 16 whenever a user is participating in a net. The CD 352initializes to a startup state 804 after the CD 352 accepts the net'ssession description by sending a SIP ACK message 808 to the CM 104. TheCD 352 transitions from the startup state 804 to a startup-wait state812 and sends a ASK request message 816 to the CM 104 immediately uponentering the startup state 812.

The CD 352 remains in a listen state 820 as long as the user does notpress the push-to-talk button 824, no PTA message 828 is received fromthe CM 104, and no sleep ZZZ message 832 is received from the CM 104.The CD 352 transitions from the listen state 820 to a floor-requeststate 836 when the user presses the push-to-talk button 824. The CD 352transitions from the listen state 820 to a talker-announce state 840when the PTA message 828 is received from the CM 104. The CD 352transitions from the listen state 820 to a dormant-idle state 844 whenthe sleep ZZZ message is 832 received from the CM 104. The CD 352transitions from the floor-request state 836 to a floor-wait state 848and sends a PTT grant request 852 to the CM 104 immediately uponentering the floor-request state 836.

The CD 352 remains in the floor-wait state 848 as long as no PTXresponse message 856 is received from the CM 104 and a PTT Abort timer860 has not expired. The CD 352 resets its PTT Abort Timer 860 and a PTTRetransmit Timer (not shown) upon entering the floor-wait state 848. TheCD 352 transitions from the floor-wait state 848 to a talk state 864 andalerts the user that the user has gained control of the net's floor whena PTX grant 868 response message is received from the CM 104. The CD 352transitions from the floor-wait state 848 to a floor-lost state 872 whenthe PTX deny message 856 is received from the CM 104. The CD 352 remainsin the floor-wait state 848 and retransmits an identical PTT request 876to the CM 104 after its PTT Retransmit Timer expires. The CD 352transitions from the floor-wait state 848 to the listen state 820 afterits PTT Abort Timer 860 expires. The CD 352 transitions from the talkstate 864 to a floor-release state 880 if the user releases thepush-to-talk button 884 while still waiting for a PTX response.

The CD 352 remains in the talk state 864 as long as no PTX interruptmessage 888 is received from the CM 104 and the user has not releasedthe push-to-talk button 884. The CD 352 transitions from the talk state864 to the floor-lost state 872 when the PTX interrupt response message888 is received from the CM 104. The CD 352 transitions from the talkstate 864 to the floor-release state 880 when the user releases thepush-to-talk button. The CD 352 remains in the talk state 864 when thePTX grant response message 868 is received from the CM 104. The CD 352transitions from the floor-lost state 872 to the listen state 820 andalerts the user 892 with a message indicating that control of the net'sfloor has been lost immediately upon entering the floor-lost state 872.

The CD 352 transitions from the floor-release state 880 to arelease-wait state 896 and sends a PTT release request 900 to the CM 104immediately upon entering the floor-request state 836. The CD 352remains in the release-wait state 896 as long as no PTX confirm responsemessage 904 is received from the CM 104 and the PTT Abort timer 860 hasnot expired. The CD 352 resets its PTT Abort Timer 860 and a PTTretransmit timer upon entering the release-wait state 896. The PTTretransmit timer is activated each time there is a PTT request orrelease.

The CD 352 transitions from the release-wait state 896 to the listenstate 820 when the PTX confirm response message 904 is received from theCM 104. The CD 352 remains in the release-wait state 896 and retransmitsan identical PTT release request 900 to the CM 104 after its PTTRetransmit Timer expires. The CD 352 transitions from the release-waitstate 896 to the listen state 820 after its PTT Abort Timer expires 860.

The CD 352 transitions from the talker-announce state 840 to the listenstate 820 and announces the talker immediately upon entering thetalker-announce state 840. The announcement can indicate that a newtalker has control of the floor, the current talker has released thefloor, or that no talker currently has control of the floor.

The CD 352 remains in the dormant-idle state 844 as long as no AYTrequest message 908 is received from the CM 104 and the user does notpress the push-to-talk key 824. The CD 352 transitions from thedormant-idle state 844 to the dormant-wakeup state 912 when the AYTrequest message 908 is received from the CM 104. The CD 352 transitionsfrom the dormant-idle state 844 to the floor-request state 836 when theuser presses the push-to-talk key 824.

The CD 352 discards any sleep ZZZ message 916 received while in thedormant-idle state 844. The CD 352 transitions from the dormant-wakeupstate 912 to the listen state 820 and sends an IAH response message 916to the CM 104 immediately upon entering the dormant-wakeup state.

Upon receipt of an AYT ping request 920 received from the CM 104 whilein any state other than the dormant-idle state 844, the CD 352 saves itscurrent state, temporarily transitions to an IAH-reply state 924, buildsand sends an IAH response message 928 to the CM 104, and return to itsprevious state. The CM 104 sends an ERR response 932 to the CD 352 whenit receives a media signaling error and enters an error state 936, suchas an malformed request making use of invalid or reserved field values.

Upon receipt of the ERR response 932 received from the CM 104 while inany state, the CD 352 alerts the user that an error has occurred,disables the CD 352 (940), and perform any appropriate SIP signaling togracefully end its participation in the net 944.

When the CD 352 has entered one of the dormant state 844, the CD 352 mayreceive point-to-point voice services calls via another IS-707 serviceoption, yet remain participants of a dormant net. After the voiceservices call is terminated, the CD 352 returns to the IS-707.5dormant/idle state 844.

However, if the net comes out of the dormant state 844 while the CD 352has chosen to receive a point-to-point voice service option call, the CD352 may miss the AYT “wake-up” message request 908 and be removed fromthe list of active participants. In such instances, the CD 352 maydetermine its participant status by sending the CM 104 an ASK request382. Once the CD 352 has been removed from the net's list of activeparticipants, the CD 352 re-registers with the CM 104's SIP server inorder to once again participate in the net.

The CD 352 allows the user to originate and receive conventional PSTNpoint-to-point calls as well as participate in group servicesdiscussions. Although the CD 352 may internally operate in one ofseveral modes, the CD 352 avoids restricting certain functionalitywithin the context of distinct operating modes that the user is requiredto explicitly navigate. Thus, seamless receipt and placement ofpoint-to-point voice-services calls while group services are enabled andactivated.

The CD 352 may be used to place a point-to-point voice services orsecure point-to-point packet voice calls at any time, whether groupservices are active or not, as long as the CD 352 is not simultaneouslyacting as a talker. If the CD 352 has registered as a member of a net,the CD 352 unregisters from the net. If the selected point-to-point callis placed via a voice service option, the CD 352 terminates dataservices. Once the point-to-point call has been completed, the CD 352may transparently enable packet data service and reregister as a memberof the current selected net.

The CD 352 may be used to receive PSTN or secure point-to-point packetvoice calls while group-services is enabled, within the limitationsimposed by the cellular infrastructure. If the CD 352 joined a net, andthe selected net is active, the CD 352 appears busy to an incoming PSTNcall and the call is given the appropriate busy treatment by thecellular infrastructure. If the selected net is quiet but the net'shang-time 620 has not expired, the call is also given the normal busytreatment by the cellular infrastructure. However, if the selected net'shang-time 620 has expired, the net has been placed in dormant mode 618,and the CD 352 has released its over-the-air resources, the call may notbe given busy treatment by the infrastructure and the CD 352 may bepaged to initiate receipt of the incoming call.

While a voice services call is active, the CD 352 is unable to receiveany NBS net traffic. After a voice services call has been completed, theCD 352 may be required to rejoin the net as it may have missed one ormore AYT requests 716. Whenever the CD 352 appears busy to an incomingvoice services call, the caller is redirected based on whatever busytreatment has been defined for the called CD 352 (such call forwarding,voice mail, etc.) by the cellular infrastructure, as expected. A usermay optionally configure the CD 352 to disable receipt of incomingpoint-to-point calls while a net is selected and the CD 352 isregistered as a member.

The CD 352 also detects if its IP network address has or is about to bechanged. If the CD 352 is participating in a net when the address changeoccurs, the CD 352 again INVITE itself to the net, as discussed withrespect to FIG. 11.

For example, a roaming CD 352 may switch cellular systems or cellularnetworks and thus negotiates a new IP network address. Or, the CD 352may experience a service disruption or drop the packet data serviceoption call for any reason and upon re-establishing service be assigneda new IP network address. If the CD 352 is participating in a net duringan address change and does not rejoin the selected net in a timelyfashion, the CM 104 eventually expires its membership and removes the CD352 from the list for the selected net. The CD 352 is removed from thelist of active net participants if it does not eventually respond to aseries of media signaling AYT request messages 716.

In the absence of the IS-707.5 Packet Data Service Option, the NBS mayoperate over the existing and commonly available Quick Net Connect (QNC)packet service. However, QNC does not currently support dormancy.Accordingly, application level messages such as “go dormant” may beignored by a CD 352 operating NBS over QNC.

QNC does provide a protocol stack similar to that provided by IS-707.5.The CD 352 may be configured to negotiate a packet connection using QNCrather than IS-707.5, and, if the QNC service is available, treats theconnection as a packet data service option connection without dormancyor, optionally, CRTP header compression support.

Under Mobile IP, the CD 352 connects to the network using a foreignagent, which assigns the mobile a care-of address. The care-of addressis temporary but legal address to which IP datagrams may be addressedfrom anywhere on the Internet. The mobile uses the care-of address tocontact its home agent and inform it of the mobile's current care-ofaddress. After confirming the identify of the mobile, the home agentthen sends packets addressed to the mobile's permanent home address(which normal Internet routing mechanisms delivers to the home agentdirectly or to the home agent's network) to the mobile using themobile's care-of address.

Although NBS can operate over Mobile IP, Mobile IP may potentiallyadversely impact the end-to-end latency and perceived voice quality ofNBS media traffic and signaling. This may be in particular ofsignificance if the CD 352 joins a net using its permanent address andthe home agent is located far, in a network topology sense, from the CM104 and the CD 352. In such a case, media traffic may optionally berouted over the public Internet or other variable quality of servicenetworks, which may not have been required if Mobile IP was not used. Toavoid this, it is preferable for the CD 352 to access NBS services usingits care-of address and rejoin nets when its care-of address changes.

Both SIP call signaling and PGP public key encryption use a unique CD352 user-id or similar unique identifier. The user database 232 definesan internal user identifier, which may be forwarded to and used by theCD 352 in media signaling requests. The CD 352 user-id addresspreferably does not contain any private data whose public disclosuremight compromise the existing cellular infrastructure authenticationmechanisms.

The CD 352 user address is used in the headers in SIP registration andinvitation, and may be used to form other parts of the required SIPsyntax. The user address is also an input to the generation of theprivate PGP key used to authenticate SIP requests. The CD 352user-interface allows the user to view the user address. The CD 352user-interface may allow the user to change the user address, at therisk of potentially disrupting the ability to access NBS or satisfy SIPauthentication requests.

To guard against certain denial of service attacks and prevent CD 352masquerading, the CM 104 may optionally request that the CD 352authenticate itself prior to registering or joining a net. Authorizationis performed at the application level, independent of otherauthorization schemes that may exist at the network or cellularinfrastructure level. CD 352 authorization is also implemented, andoperates, independently of concepts and data structures supportingencrypted (secure) NBS nets.

In particular, the CM 104 may request that the CD 352 include an“Authorization” header with its SIP requests. The authorization headerallows for the SIP message to be signed by the CD 352 using PGP publickey cryptography signatures.

Public key cryptography generates a public and private key from aprivate secret key, typically known only to the encryptor (in this case,the CD 352). The private key, in combination with the secret, isrequired to sign a message, but the public key alone can be used toverify a signed message's signature. Thus, to support SIP authorization,each CD 352 is preferably provisioned with a private secret and privatekey, which are never shared. Each CM 104 to which the CD 352 may need toauthorize itself should know the public key of the CD 352. Since thepublic key is not secret, it may be stored as part of the user portionof the database 232 maintained by the CM 104, or accessed throughgeneric public key servers on the Internet.

The CM 104 may require CD 352 authorization at the server, net, or userlevel. At the server level, the CM 104 requires all clients connectingto the CM 104's SIP server 236 (see FIG. 3) to provide authorizationcredentials, rejecting all requests that are not authorized. When serverlevel authorization is enabled, only clients whose identities (i.e., aclient's public key) are previously known to the CM 104 may effectivelyuse the server. Server level authorization can protect the CM 104 SIP'sserver 236 from many relatively easy denial-of-service attacks.

A CM 104 may protect one or more nets it manages through authorization,but leave other nets “unprotected.” If the CD 352 attempts to INVITEitself to a protected net, the CM 104's SIP server 236 rejects therequest unless the CD 352 can be authorized by the CM 104.

Also, the CM 104 may use authorization to insure that the CD 352 (or anySIP user-agent client in general) does not attempt to masquerade asanother CD 352 and hence either deny service to legitimate netparticipants or passively monitor a net's media channels. If the CM 104requires that a specific CD 352 be authorized, the CM 104 does notaccept any SIP requests from a client connecting as the CD 352 unlessthe client's SIP requests include a PGP signature that may be verifiedby the CM 104. At the user level, authentication may be configured on aper user basis (i.e., the CM 104 may require that certain users beauthenticated before while allowing other users to remainunauthenticated).

The PGP private key may either be administratively provisioned within orcreated by the CD 352, once the CD 352 user address is defined. Theprivate key need not be stored externally, but the associated public keyis generally loadable into the user portion of the database 232 of anySIP server requiring CD 352 authentication.

In an embodiment, the primary NBS CD 352 or net participant platform isa CD 352 MA based cellular handset. Because NBS is built over IP and IPtransport protocols, any IP capable platform with connectivity to the CM104 may potentially serve as a NBS CD 352. Accordingly, dial-up usersmay connect to the CM 104 via the PSTN through existing IPterminal-servers operated by Internet Service Providers (ISP), asillustrated in FIG. 1. The terminal-server acts as a bridge between thePSTN and a LAN supporting IP. The terminal-server comprises a bank ofmodems, which provide a connection point for high-speed PSTN modems, aserver, and one or more network interfaces. The server is capable ofhosting multiple independent PPP sessions, one for each connected modemuser. The server also acts as a router, routing IP packets between eachof the individual PPP interfaces and any active LAN interfaces. The CM104 either includes an integrated (or be deployed in conjunction with anexternal) commercial off-the-shelf terminal-server.

The dial-up terminal server supports and includes the ability tonegotiate CRTP Header Compression over its PPP sessions. Similarly, thePPP stack used by a dial-up client also includes and attempts to useCRTP. However, because of the additional bandwidth available overhigh-speed modems, the inability for a dial-up based user to negotiateCRTP Header Compression may not necessarily force a net to avoid usingRTP based payload specifications.

If the terminal-server is located on a CD 352 MA service provider'sinternal LAN, and hence near, in a network topology sense, to theservice provider's CM 104, dial-up users may avoid quality-of-serviceissues that may contribute to high end-to-end latency if the pathbetween the ISP's terminal-server and the CM 104 traverse a portion ofthe public Internet. Since PSTN based modems typically do not support adormancy concept similar to that implemented by IS-707.5, dial-up basednet participants ignore any sleep messages received from the CM 104.Although the user database 232 tracks whether a connecting user iscellular or land based, this facility is still provided. Accordingly,the CM 104 may or may not send sleep or other media-signaling messagesto dial-up users.

NBS service areas is designed to be integrated, both to allow users toroam between service areas as well as to join equivalent nets definedwithin separate service areas. Peer-to-peer communications betweenmultiple CMs 104 takes the form of SIP server redirects, the exchange ofuser and net database records, and additional messages specific to anintegrated NBS service.

In an integrated NBS service embodiment, it may be preferable to allowany CM 104 to assume ownership of a net. Thus, operation of a net is notspecific to a particular CM 104 or MCU node 208. The choice of CM 104may be determined dynamically, based on factors such as proximity to themajority of net participants and available quality of service on aservice providers inter-system network. Similarly, any SIP redirectserver 236 is capable of redirecting any CD 352 to the appropriate MCU'sSIP user-agent server, and/or, if necessary, forwarding the CD 352 toanother SIP redirect server.

In an integrated NBS service embodiment, a net's net-address has meaningthroughout the NBS system. As a result, one or more top-level SIPservers 236 are responsible for redirecting INVITE requests anddistributing net participants to the appropriate MCU nodes 208. Thetop-level SIP servers 236 may share a common user and net database 232,providing similar functionality and redirection decisions at differentnetwork rendezvous points. As a result, the redirection of CD 352originated invitations provides an important and critical layer ofabstraction that allows multiple CM 104 installations to be integratedinto a single homogeneous NBS service.

In an integrated NBS service, the system scales by duplicating thefunctionality provided by the MCU node manager 256, its associated setof MCUs 252 (loosely termed an “MCU Cluster”), including its SIPuser-agent server. A single database 232 and administration interface248 is shared by all elements of the system.

The process by which a CD 352 joins a net in such an integrated systemis substantially the same as to that used in a system comprised of asingle CM 104 installation. The CD 352 initially sends all SIP requeststo the top-level (now global) SIP redirect server 236. The redirectserver 236 redirects, via SIP mechanisms, the requesting CD 352 to theappropriate destination. In the case of an INVITE request to join a net,the destination is the SIP user-agent server 252 associated with the MCUnode 208 with current responsibility for the net in question. In thecase of an INVITE requesting a current list of nets available to the CD352, the destination is any user-agent capable of responding to therequest.

Separately, the redirect server 236 may exchange additional messageswith the MCU 252 via inter-application messaging usingimplementation-specific protocols and/or messaging conventions. As inthe non-integrated case, special startup action may be necessary toensure that the redirect server 236 may determine a destination forevery legitimate INVITE requests it receives. One embodiment has the SIPregistrations existing at the top-level redirect server 236. Also, thetop-level server may query the system database and attempt to map eachinvitation request to a net definition contained therein.

The CD 352 may offer encrypted net broadcast communications. At theoption of net users, voice and data transmitted on a particular net maybe encrypted at the transmitting CD 352, and decrypted by all other CDson the net. Encryption is end-to-end, i.e., from CD to another. Netcommunications are typically encrypted by a commercial encryptionalgorithm incorporated in a NBS capable CD. The choice of whether a CD352 treats a net as encrypted or unencrypted is at the discretion of thenet users; that is, involvement of the CM 104 is not required.

Users may select on a net by net basis whether they would prefer traffictransmitted/received on that net to be encrypted/decrypted. The user isgiven the capability to enter an encryption key for the net using, forexample, the phone keypad. The user is thus be capable of engaging inencrypted communications with other users of the net who have alsoselected the encryption option for that net and who are also using thesame encryption key.

The user may enable or disable the encryption of net traffic for any netkey that the user has entered into the CD 352 at any time. Media trafficmay be symmetrically encrypted through the use of a symmetric key (atraffic encryption key, or TEK) that is shared by net users. Net trafficencryption keys may be generated off-line by a net user or netadministrator and then securely distributed to net participants whomanually enter the keys into their respective communication devices. Thekey is used for media traffic over a particular net, until new keys aregenerated and distributed to the net users to replace the previous netTEK.

The CD 352 is notified that it is a member of a particular net throughmessages received from the CM 104. The net administrator for a specificnet may set an advisory flag that indicates that the net is intended tobe encrypted. This indication is generally advisory, and does notnecessarily authoritatively indicate that communications on the net areactually encrypted. The CD 352 user interface allows a user to designateany net as an encrypted net, and allow the user to input the net TEKfrom the CD 352, independently of whether an encrypted advisory flag forthe net has been received by the CM 104.

The CD 352 may enforce minimum and maximum key lengths. The CD 352 mayprovide a means for a key checksum to be input along with the key, andif provided, to check the checksum against the key entered. If thechecksum is not entered, the CD 352 calculates the checksum and makes itavailable for display to the user. The CD 352 does not necessarilydisplay the key on the CD 352 display after initial key entry.

Once a key is successfully entered for a given net, media transmissionson the net is encrypted using that particular key, and all trafficreceived on the net is decrypted using that particular key. Theencrypted traffic includes additional headers that allow the CD 352 tosynchronize the encryption/decryption process, to allow for latesynchronization (synchronization to a transmission already in progress),and to confirm that the sender and receiver are using identical trafficencryption keys. If a CD 352 receives encrypted traffic (detected by thepresence of the encryption headers) on a net that it has not designatedas encrypted, the CD 352 indicates that it is receiving encryptedtraffic to the user, and does not output traffic (mute the audio orsuppress data output). Similarly, if the CD 352 receives media trafficthat is not encrypted on a net for which it is configured to encrypt, orif the traffic is not decrypted correctly (for instance if the keys areincompatible) the CD 352 alerts the user and mute the traffic.

The key for an encrypted net may simply be a random (binary) number. Ingeneral, the key may be generated by one party in a net, or anadministrator for that net, and distributed securely to the netparticipants. Since the key distribution policy is currently left to thenet users, it is a potential source of compromise of the net security.Thus, it is recommended that the net encryption key be distributed usingsecure means, such as PGP encrypted e-mail, to the net participants. Thesecurity manager 20 (FIG. 1) also provides a central repository forcommon net keys. Other methods are also possible, such as a standardtelephone call or face-to-face meeting. Keys may also be distributedautomatically to CDs, using an imbedded PGP secret key into acommunication device for SIP authentication.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

Other features and advantages of the invention are set forth in thefollowing claims.

1. In a communication device, a method for reducing latency in a groupcommunication network, the method comprising: receiving a request from auser of the communication device wishing to initiate a group call;receiving media from the user before processing the request; bufferingthe received media for later transmission to a controller; and signalingthe user to stop sending media if a memory unit used for buffering thereceived media runs out of space before the request is completelyprocessed and media communication is not established between thecommunication device and the controller.
 2. The method of claim 1,further including: transmitting the buffered media to a target receiverif a memory unit used for buffering the received media runs out of spacebefore the request is processed but media communication is establishedbetween the communication device and the controller.
 3. A communicationdevice for reducing latency in a group communication network, thecommunication device comprising: a receiver to receive a request from auser who wishes to initiate a group call; a memory unit to buffer mediathat is received from the user before the request is processed; atransmitter for transmitting the buffered data to a controller after therequest is processed; and a processor for processing the receivedrequest and the media, the processor being communicatively coupled withthe receiver, the memory unit, and the transmitter wherein the processorsignals the user to stop sending media if a memory unit used forbuffering the received media runs out of space before the request iscompletely processed and media communication is not established betweenthe communication device and the controller.
 4. The communication deviceof claim 3, wherein the transmitter transmits the buffered media to atarget receiver if a memory unit used for buffering the received mediaruns out of space before the request is processed but mediacommunication is established between the communication device and thecontroller.